Can I take them to the school I enrolled them in until we go to court?
You stated you have filed a motion with the court (I'm guessing) for custody modification. The children live with you, and you have enrolled them in school. He is being uncooperative (my opinion).
The safest answer here is ask your lawyer, who filed your case with the court. My opinion answer is YES, of course take those kids to school! If dad has a problem with it, deal with him in court.
I'm not a lawyer. This is only my opinion /suggestion. Most Replys' are based on information provided by the "original post" (OP).