Neither parent has legal custody

I have 2 step sons. One lives with me and his father the other with the mother. Neither one of them have any kind of legal custody set forth by the courts. Now the younger one wants to live with us. he is here for the summer. If his father goes to court will he ba able to stay with us until the case is finalized??

If there IS no custody agreement legalized by the court, either parent is presumed to have equal control and equal "say" in what happens to a child. You say "If the father goes to court"---why would the father go to court? To petition for full custody? If he does this, it is my feeling that the court would rule that the children should be together--regardless of which parent they are with. Separating young children from one another is rarely desirable.

You say "...until the case is finalized"? What case? IS there a current pending case before the court?

How old are the children? Are you married to the children's father? Is the children's mother remarried? Why is there no custody agreement? One day two people decide they don't want to be married any longer so they just move apart and separate siblings? In what state do you reside?

You simply cannot receive a precise answer without giving accurate detailed information.