Stressful ex! Please help!

So my fiancé and I have been together for almost 3 years. Both of us have been divorced. Mine was a clean divorce, his was not. He has two kids with his ex and they were married for 7 years when they divorced. His kids now are 8 and 7.  About a year after their divorce, his ex went off of the deep end when she found out he moved on and we started dating. (Backstory:: we actually dated in high school and broke up for whatever reason and got back together now) since then, she has tried everything to ruin our lives. With telling me they are sleeping together (which I know for a fact they aren't) that she was pregnant with his child (supposedly conceived in June and was due the following may.... Yes 11months haha) then when that didn't break us up, she tried to get is where it really hurts, by taking the kids away.  I have a really close relationship with the kids. I have made it very clear that I am not trying to become mommy, that nobody will ever replace their mom, and they have always understood that. I have always promoted loving both parents. Well his ex was still upset over our relationship, and over him trying to get his 50% custody, and started filing false police reports saying we hit the kids and throw them and burn them. Absolutely rediculous accusations. She filed a temp restraining order against us and we could not see the kids or talk to them for 2 months until court reconvened.  We hired a lawyer and paid $10,000 to get the kids back and to prove she's a lying piece of crap. We won our case and won the custody we were going for.  Since then, she has been violating court orders, threatening suicide, causing scenes at the girls school, making more accusations that we are poisoning them and drugging them. We have come to find out that she does not give them baths, help with homework, wash their clothes or do their hair.  They always come to us filthy.  Well more accusations have started, and I am getting fed up with it. I want it all to end. I want the drama to stop, but I don't know what to do. My fiancé says we need to wait for her to go back to court before we do anything.  But nothing bad ever seems to happen to her. It's only us that are the ones hurting. What can I do? Only serious advice please.