There are billions of Garbhodakashayi Visnus, Brahmas and Kṣīrodakaśāyī Viṣṇu (Paramatma or Supersoul), but only ONE Karanodakshayi Visnu (Maha-Visnu)

Garbhodakashayi Visnu, seen in first painting below, resides deep inside of each of the billions of gigantic "Brahmanda material universes" that come from Maha-Visnu's dreaming of the entire material creation.

Srila Prabhupada – "This material creation is the spirit soul’s dream. Actually all existence in the "material world" is a dream of Maha-Visnu." (SB, Canto 4.29.83)

All the Brahmanda universes originate from the pores of His skin and His breathing, Srimad Bhagavatam's 5th Canto explains.

These spherical Brahmanda universes all come from Karanodakshayi Visnu (Maha-Visnu) as seen in 2nd painting below.

Each Brahmanda universe surrounds and encases an inner "secondary smaller universe" where Garbhodakashayi Visnu,  Lord Brahma, Lord Siva, along with all the other demigods resides who each manage the many material elements within each "secondary material universe." 

Coming from Garbhodakashayi Visnu, who is deep inside each of the Brahmanda material universes within the "secondary smaller universe" inside them, is Lord Brahma who creates all the planetary systems in the secondary material universe as seen in 5th painting. 

All the inner material universes that are deep inside each Brahmanda, are of different sizes, our inner material universe within our our Brahmanda, is only 4 billion miles in diameter and has 14 planetary systems according to Srimad Bhagavatam's 5th Canto.

Therefore the inner universe our Garbhodakashayi Visnu is in, is very small compared to other universes that are deep inside of their Brahmanda universal shell.

In this way, there are billions of Garbhodakashayi Visnus, Brahmas and Kṣīrodakaśāyī Viṣṇu (Paramatma or Supersoul), but only ONE Karanodakshayi Visnu (Maha-Visnu)

Each inner material universe deep inside their Brahmanda, is therefore surrounded by, and encased in a massive outer shell or greater universe which is called a Brahmanda that is made up of 7 massive material layers.

As said above, all Brahmanda spherical universes, sometimes called shells or egg looking universes in Srimad Bhagavatam, originates from Maha-Visnu (Karanodakshayi Visnu) as seen in painting.

The first expansion of Lord Krsna the Supreme Personality of Godhead and cause of all causes, is Balarama and from Him, all Visnu/Narayana expansions originate.  

In the material creation, Maha Visnu, Garbhodakashayi Visnu and Kṣīrodakaśāyī Viṣṇu (Paramatma or Supersoul) all are also expansions of Balarama, manifests.

Srila Prabhupada - "Mahā-viṣṇu, enters. He lies within the Causal Ocean and breathes out innumerable universes, and into each universe the Lord again enters as Garbhodakaśāyī Viṣṇu. 

Each universe is in that way created. He still further manifests Himself as Kṣīrodakaśāyī Viṣṇu, and that Viṣṇu enters into everything—even into the minute atom. This fact is explained here. 

He enters into everything. Now, as far as the living entities are concerned, they are impregnated into this material nature, and as a result of their past deeds they take different positions. Thus the activities of this material world begin.

The activities of the different species of living beings are begun from the very moment of the creation. It is not that all is evolved His plenary parts are viṣṇu-tattva, or the Lordship of Godhead. 

From Śrī Kṛṣṇa, the next manifestation is Baladeva (Balarama)

From Baladeva (Balarama) is Saṅkarṣaṇa, from Saṅkarṣaṇa is Nārāyaṇa, from Nārāyaṇa there is the second Saṅkarṣaṇa, and from this Saṅkarṣaṇa the Viṣṇu puruṣa-avatāras. 

The Viṣṇu or the Deity of the quality of goodness in the material world is the puruṣa-avatāra known as Kṣīrodakaśāyī Viṣṇu or Paramātmā. Brahmā is the deity of rajas (passion), and Śiva of ignorance. 

They are the three departmental heads of the three qualities of this material world. 

The creation is made possible by Brahma's quality of passion and his endeavor, it is maintained by the goodness of Viṣṇu, and when it requires to be destroyed, Lord Śiva does it by the tāṇḍava-nṛtya. 

The materialists and the foolish human beings worship Brahmā and Śiva respectively." (SB, Canto 1:2:23 - purport)

From Maha-Visnu's breathing and through the pores of His skin, all the individual massive universes (Brahmandas) manifest.

The diameter of our outer Brahmanda universal shell is 44 quadrillion 444 trillion 444 billion miles in diameter, or twice that size if the measurement is taken from one side of the inner secondary universe inside the Brahmanda.  

There are many other Brahmanda universes much larger than ours. So, yes ours could be twice that size if measured from the outer edge of our inner material universe.

So lets be clear, deep inside each Brahmanda universal shell is found Garbhodakashayi Visnu, from Him Lord Brahma appears on top of a lotus stem on a lotus flower growing from Garbhodakashayi Visnu's naval.

And from Brahma comes all the different planetary systems within his particular individual material universe (an unlimited number)

As already said, there are billions of Lord Brahmas each managing their own inner material universe deep within their Brahmanda.

Also Maha-Visnu expands again to a third Visnu known as Ksirodakashayi Visnu who is the supersoul that is within the heart of all material bodily vessels that the marginal living entities (jiva-souls) are given by Maha-Visnu.

The material bodily vessels the jiva-souls occupy in the material creation are "hired" from Maha Visnu's dreams by the visiting jiva-souls.  

The entire material creation is the dreams of Maha-Visnu according to Srimad Bhagavatam, everything conceivable He dreams - EVERYTHING is covered in Maha-Visnu's dreams.

Srila Prabhupada – "This material creation is the spirit soul’s dream. Actually all existence in the material world is a dream of Maha-Visnu, as the Brahma-Samhita describes-

"This material world is created by the dreaming of Maha-Visnu. The real, factual platform is the spiritual world, but when the spirit soul wants to imitate the Supreme Personality of Godhead, he is put into this dreamland of material creation." (SB, Canto 4 Ch 29 text 83)

Srila Prabhupada – "Everything happening within time, which consists of past, present and future, is merely a dream. This is the secret in understanding in all the Vedic literature." (SB, Canto 4.29.2b)

Srila Prabhupada – "Our contact with matter is just like dream. Actually we are not fallen. Therefore, because we are not fallen, at any moment we can revive our Krsna consciousness, we break the dream." (Tokyo Japan 1972: SB, Canto 2.9.1)

Srila Prabhupada – "Factually all of material existence is only a dream. Thus there is no question of past, present or future. Persons who are addicted to karma-kanda-vicara, which means ‘working for future happiness through fruitive activities’, are also dreaming. Similarly, past happiness and present happiness are merely dreams." (SB, Canto 4.29.2b)

The jiva-soul are NOT part of Maha-Visnu's dream, only the material bodily vessel are from the dreams of Maha-Visnu.

All material bodies belong to Maha-Visnu that we, jiva-souls, get from Maha-Visnu so we can experience our rebellious material desires while trying to enjoy separate from Krsna in the temporary decaying material creation.

This material creation is NOT the jiva-soul's real home, our real home is Vaikuntha or Goloka Vrindavan in the perpetual spiritual world.

Maha-Visna's dreaming creates the material worlds (Brahmandas) that provides material facilities and material bodies to the jiva-souls who have chosen to enter the material creation.

No jiva souls originate from Maha-Visnu, they instead go through Him after leaving Vaikuntha Prabhupada has explained to us.

Maha-Visnu then plants the jiva-soul in a suitable material body on a suitable planet according to each jiva-soul's material desires.

But the jiva-souls existence in the material creation is also their dream according to Srimad Bhagavatam, a dream within a dream.××