I have 1 niece and 4 nephews in foster care. I just found out that they were taken from their mom. I would love to take custody of them but unfortunately I don't have the room for all of them. I figure if I get to have visitations with them at least I can still be in their lives, and they can contact me when they need. So who do I contact to ask this question?

No a aunt or uncle have no legal visit rights.

You could ask the foster care case worker if they would let you,