Maha-Visnu's massive Brahmanda universes originate from His breathing and from the pores of His skin.

Deep inside each Brahmanda universe is a secondary universe where Maha-Visnu expands as Garbhodakashayi Visnu.

From Garbhodakasayi Visnu deep inside each Brahmanda, a Lord Brahma appears and builds the planetary systems within his inner material universe.

There is only one Maha-Visnu in the material creation however, there are billions of Garbhodakashayi Visnus and Lord Brahmas because of the secondary material universe existing within each Brahmanda universe.

Both Garbhodakashayi Visnu and Brahma are within their own secondary universe and there are billions of them inside the material creation.

Each "inner material universe" houses Garbhodakashayi Visnu, Brahma, and many planetary systems (14 in our universe) 

This means our universe is surrounded and encased by the greater Brahmanda universal shell that originates, with billions of other Brahmandas, from Maha-Visnu as seen in painting below.*^*.