Hello

My grandson and nephew both have babies from two different young girls both young men sign the birth certicate who has the legal right of the child.(2) If dface ever take either child out of the home who is next in line to get the child? Do either father has to be investagate before he can get the child?

If they get taken off them they would have to step in and let DFS know they want to kids.
DFS might ask but it is better to be proactive and show that you want them. They could investigate they might not, but most likely would.

They have the same legal rights as ANY father. If DFS finds cause to remove the child from the care of the mother, then they can petition the court for primary custody.