Welcome to Just Answer. I am here to help you resolve your tax and finance concerns. Please feel free to ask anytime you need extra help.
First, if the couple files a joint tax return the refund (up to all of it) can be taken to help reduce the student loan obligation. The only way around this is to file married separate. However, then your husband will not be able to claim you.
Second, as to the claiming of the children.If they are dependents of either of the two of you they can be claimed by either of you so long as you (together) are married by the end of the year and provided more than 1/2 their support. If a former spouse is claiming them, then you cannot.