Aaaaw, somebody played ABBA!
Oh love, I can barely think of words. Let's pretend that I opened this reply with something that gives your painful situation the respect and gravity it deserves. I'm so sorry for what you're going through.
I'm in Australia; that might explain why I can't understand why your will can't be 'your will'. As far as I know, if you have a will that says you want your billion dollar mansion kept in trust to give your goldfish a nice place to live out it's days in, your kids would have to just accept it. A will is a will; you can will your estate to anybody. Talk to a lawyer. But okay if you can't, your idea re selling up and giving him the cash is spectacular. Also, get a nice fat credit card and run up an around-the-world trip on it. Your estate can be a great huge debt. See if they're interested in it then.
Sorry... if you can, for a while put the thoughts about the kids in another place. You two are the most important things. Do your chemo. Live your life.