besides the trauma that all of you have to deal with now because of this perp, you do have a chance to get him in jail.
even if he doesnt go to jail, he at least has to answer questions by officials, has to take SOME responsibility for what he has done. fact is, the victims (little kids) have not done anything wrong but he has. regarding that, the kids have a right that someone fights for their rights. they need to know that they were not at fault but the stepdad was. thats essential to their healing. you are doing everything right.
its always uncomfortable, as only very few perps just admit what they have done, which means the kids might be asked (with a psychologist most probably...) but that too shows them, if done the right way, that they were not at fault and that someone cares for them.
i really with you all the luck in the world to go thru this. you are a fighter for the right of the kids and the kids are lucky to have you. most of the times noone ever finds out and the kids never feel any sort of justice is done, not even someone saying: it wasnt about you, the person is a perp and he would have abused anyone he had the opportunity to do so.

keep it up!
( i also faught for my daughter, who was abused by her believe it or not, but things do get better! never forget that!)
everything is always okay in the end, if it's not, then it's not the end