Legal Question in Family Law in Texas

The birth of the new baby drops his percentage from 25% to 22.5% (not much). You'll probably find that if you recalculate what child support should be, based on his current income, there won't be any reduction in his child support (if you went back to court on a motion for modification).

Are you planning to sue for custody of only ONE of the two sisters? That in itself creates problems.

Under the new law (effective September 1), a 12-year-old no longer gets to file a "choice of managing conservator" with the court. The legislature did away with it.

But to answer your question: The Texas Family Code doesn't definitively address a situation where one parent has custody of one sibling and the other parent has custody of the other sibling. What the courts usually do is (a) set Dad's child support for ONE child based on all his circumstances (income, other children he's responsible for who live with him) and (b) set Mom's child support that she owes Dad for the child that doesn't live with her, based on all HER circumstances, and one parent pays the other parent the difference each month (it could end up being $38.13).

Other judges simply say, "One child to each parent ... it's a wash. No child support."