In Gauḍīya Vaisnavism there are three different forms of Visnu-tattvas who manage the temporary material creation.

 1 - Mahā-Visnu (Kāraṇodakaśāyī Visnu)  

2 - Garbhodakaśāyī Visnu (Hiraņyagarbha)  

3 - Ksirodakaśāyī Visnu (Paramātmā or Supersoul).

Maha-Visnu (Kāraṇodakaśāyī Visnu) is ultimately an expansion of Lord Balarama, the first expansion of Lord Krsna the Supreme Personality of Godhead, the Absolute truth, and cause of all causes.

Krsna is an individual Person AS a spiritual bodily form with 2 arms, two legs etc in His original and perpetual appearance.

And all marginal living entities (jiva-tattva souls) in their original bodily form, are in His image Prabhupada explains here.

Devotee – “Is the original body of the spirit soul a human form?”

Srila Prabhupada – “Yes, human form. God is also human form. "Man is made after the shape of God." I think there is in the Bible. Is it not? So God is also like human form. Here you see Krsna, two hands, two legs."

Hari-sauri – "How do we understand, then, that there are peacocks and flowers and trees in the spiritual world? Are these not eternal forms?"

Srila Prabhupada – [describing material form first]: "Yes, they are more covered, just like if you cover your body with blanket, the hands and legs are invisible. But you are not the blanket. So the trees and plants, they are more covered. They are not in full manifestation. The human form is the full manifestation of the jiva-soul.?"

Hari-sauri - “They are covered in the spiritual world?”

Srila Prabhupada - “Not in the spiritual world, there that is voluntary. Some devotees want to serve Krsna as flower; so they become flower there if they want to be a flower and lie down at the lotus feet of Krsna, then he becomes flower, voluntarily, and he can change from flower to human body also. That is spiritual life. There is no restriction. If some devotee wants to serve Krsna as cow, he serves Krsna as cow, as calf, as flower, as plant, as water, as ground, field, or as father, as mother, as friend, as beloved, anything. It is inconceivable, yet a fact." (SB, Canto 6 Ch 1 text 1-4 Melb, Australia May 20, 1975)

In Gauḍīya Vaisnavism, a school of Vaiṣṇavism, the Sātvata-tantra describes three different forms, or aspects, of Visnu as-

1 - Mahā-Visnu (Kāraṇodakaśāyī Visnu)

2 - Garbhodakaśāyī Visnu (Hiraņyagarbha)

3 - Ksirodakaśāyī Visnu (Paramātmā or Supersoul).

Maha-visnu further expands as the form of  Garbhodakaśāyī Visnu (Hiraņyagarbha) and enters each of the millions of large universes known as a "Brahmandas" that all originate from the pores of Maha-Visnu's Body, who lays down deep inside each of these massive "Brahmanda" individual outer material surrounding universes.

Maha-Visnu again further expands as Kṣīrodakaśāyī Visnu (Paramatma) who is the Supersoul situated in the heart of all material bodily vessels next to the living beings (jiva-souls) in all the millions of material universes.

Kāraņodaksayi Visnu is Sankarsana (an expansion of Balarama) of the Catur-vyuha, the quadruple expansions of Krsna who predominate over the Vaikuṇṭha planets as His Visnu-tattva expansions.

Balarama is the first expansion of Lord Krsna who the Supreme Personality of Godhead and cause of all causes, and origin of all Narayana and Visnu forms of the Lord.

So, all the demigods such as Brahma and Siva, as well as all the material bodily vessels that the visiting jiva-souls possess, are part and parcel of Maha-Visnu "dreaming" material creation including within all the different secondary material universes found deep within each Brahmanda greater universe.

Maha-Visnu creates all the material bodily vessels or containers that are eventually occupied or possessed by all the visiting jiva-souls who have chosen to leave Vaikuntha and foolishly enter the mundane decaying material creation, which is 1/4 of the Brahmajyoti or Spiritual Sky.

No jiva-souls originate from the material creation, or from Maha-Visnu, or the impersonal (dormant inactive condition) aspect of Brahmajyoti or Brahman.

This is because ALL jiva-souls originate directly from Vaikuntha, from Goloka Vrindavana.

Also the original FORM of the marginal living entity or jiva-souls is NOT some nonsense impersonal spark in Krsna's effulgence (impersonal Brahmajyoti)

The Jiva-soul is ORIGINALLY a 2 armed bodily (vigraha) form like Krsnas Prabhupada has explained above owever, many Sangas (religious groups), cannot understand this.

The full potential and highest understanding of the jiva-soul is -

1 - Sat - eternity 

2 - Cit - knowledge 

3 - Ananda - bliss

4 - Vigraha - spiritual bodily form

Maha-Visnu in His material creation, lays down in the causal ocean or the Karanodak, He then puts the seeds of this material creation in Mahā-māyā by glancing at her.

Mahā-māyā remains the ever obedient material energy of the Supreme Lord.

Maha-Visnu creates all the material elements -

1 - Sky,

2 - Fire,

3 - Water,

4 - Air,

5 - Earth,

These material elements are created along with -

6 - Mind,

7 - Intelligence,

8 - False ego.

After this, Maha-Visnu enters each of the larger universes known as a Brahmandas, that originate from the pores of His Body, as Garbhodaksayi Visnu, who lays down deep inside each surrounding Brahmanda universe, in a secondary smaller universe within it.

Garbhodakasayi Visnu is an expansion of Maha-Visnu, there are billions of Garbhodakashayi Visnus and Lord Brahmas but only one Maha-Visnu (Kāraṇodakaśāyī Visnu).

All jiva-souls (marginal living entities) are individual independent living entities who can choose to enter this material creation, to the smaller material universe that exists with all its 14 planetary systems in the stem growing from the navel of Garbhodakasayi Visnu who are all encased deep inside the surrounding Brahmanda universe.

From Garbhodaksayi Visnu emerges Brahma who is the secondary creator within His secondary universe that is deep inside the outer surrounding Brahmanda universe.

Garbhodakaśāyī Visnu is an expansion of Mahā-Visnu.

In Gaudīya Vaisnavism the Sātvata-tantra describes three different forms of Visnu as-

1 - Mahā-Visnu (Kāraṇodakaśāyī Visnu)

2 - Garbhodakaśāyī Visnu (Hiraņyagarbha)

3 - Ksirodakaśāyī Visnu (Paramātmā or Supersoul).

Srila Prabhupada - "The science of God analyzes the constitutional position of God and His diverse energies. Material nature is called prakṛti, or the energy of the Lord in His different puruṣa incarnations (expansions) as described in the Sātvata-tantra-

viṣṇos tu trīṇi rūpāṇipuruṣākhyāny atho viduḥekaṁ tu mahataḥ sraṣṭṛdvitīyaṁ tv aṇḍa-saṁsthitamtṛtīyaṁ sarva-bhūta-sthaṁtāni jñātvā vimucyate

"For material creation, Lord Kṛṣṇa's plenary expansion assumes three Viṣṇus. 

1 - The first one, Mahā-Viṣṇu, creates the total material energy, known as the mahat-tattva. 

2 - The second, Garbhodakaśāyī Viṣṇu, enters into all the universes to create diversities in each of them. 

3 - The third, Kṣīrodakaśāyī Viṣṇu, is diffused as the all-pervading Supersoul in all the universes and is known as Paramātmā. He is present even within the atoms. Anyone who knows these three Viṣṇus can be liberated from material entanglement." (BG, Ch 7 text 4 Purport)

Each Visnu-tattva form has a different role in the maintenance of the Universe and its inhabitants.

1 - For material creation, Lord Krsna's plenary expansion assumes three Visnus. The first, Mahā-Viṣṇu, creates the total material energy, known as the mahat-tattva and all the Brahmanda universe as seen in painting below.

2 - The second, Garbhodakaśāyī Viṣṇu, enters deep inside of each of these massive Brahmanda  universes, reaching its center, and then creates a secondary inner universe with all its diversities.

3 - The third, Kṣīrodakaśāyī Visnu, is diffused as the all-pervading super soul in all the universes; in the heart of every living being, is known as Paramātmā. He is present even within the atoms.

The real objective of meditation in Yoga is attain service to Krsna the Supreme Personality of Godhead and cause of all causes.

Garbhodhakaśāyī Visnu is also realized as the form of Pradyumna within the material universe who the father of Brahmā who appeared from His navel and hence Garbhodakashayi Visnu is also called Hiraņyagarbha.

There are billions of Brahmanda universes all originating from the Body of Maha-Visnu. 

Inside each Brahmanda universe is a secondary smaller universe where Garbhodakashayi Visnu, Lord Brahma and all the different planetary systems are found. 

The inner material universe is managed by Brahma, it is surrounded and encased by the outer Brahmanda universe's 7 massive material layers. 

Our Brahmanda universe alone measures 44 quadrillion, 444 trillion, 444 billion miles in diameter, or twice that size if measured from the outer edge of the inner secondary universe inside the Brahmanda.

All the unlimited number of Brahmanda material universes are different sizes making their inner secondary material universe inside them also a different size.

The size of each material universe inside the Brahmanda is determined by the amount of heads each Brahma has.

Our material universe is small because our Brahma has only 4 heads, other universe inside their Brahmanda, their Lord  Brahma may have 10, 30,  50, 500, 10,000 or even a million heads according to Srimad Bhagavatam.

Also there are the 14 planetary systems (shown below in photo) in our material universe situated deep within our surrounding Brahmanda. 

However, other universe have many more planetary systems, depending on how many heads their Lord Brahma has.

There are billions of these Brahmanda universes, all coming from the Body of Maha-Visnu as seen in painting below.

As said above, each Brahmanda has their own "secondary inner material universe" deep inside their Brahmanda.

And each inner secondary universe has their own number of Planetary System that are all in different sizes.

Ours has 14 different planetary systems while other universe may have hundreds of planetary systems.

This means there are billions of Garbhodakashayi Visnus, billions of Lord Brahmas, billions of Lord Sivas, billions of Indrus, billions of all the demigods in each universe that is deep inside their own outer Brahmanda greater universe.

However, there is only ONE Maha-Visnu as seen in painting below.*^^*.