Get a good lawyer and figure out how you can document *anything* and *everything* to the contrary of his claims. It's hard to believe that your family would be against you if the accusations were false, but I guess some families aren't made up of the best, most supportive people, so I hope the truth comes out either way.
Think of any emails you have, doctors records, school records, school notes, anything you might have that will show that you are a good parent and bring everything with you.