Which of these issues can a mediator help work out?

The whole idea of mediation is that it is more cost effective for you not to have to retain a lawyer. It does require compromise and cooperation to be successful and fair to all parties. If you want to duke it out and win a bigger part of the pie, then mediation is not the place for you and if you are going to resent her parents for attending etc...you also should go by way of a regular court because you aren't going to be happy in mediation. In mediation civilized, reasonable, people come together to settle things in a mature and fair way. If you don't wish to play fair, hire a really good lawyer.