Brother Keeps Stalling About Getting Will Done

My brother went through a bitter divorce, she got custody of the kids, but the kids are in my home everyday now (brother and I share ownership of the house and mom lives with us) even though my brother has visitation rights every other weekend and on Wednesday nights. He is also contributing more money to the kids than he is legally required to, but when we need things for the house, like a new garage door, he tells me he has no money. When I tell him I don't want to hear he has no money since he is spending more money on his kids than the court ordered, he tells me it's none of my business.
If it weren't for me doing one year of paperwork and talking to accountants and lawyers, his ex would have gotten a lot more money from our house than she did, everything I did was legal, but I was the one who did all the work to save his hide, not him, so I feel a little betrayed now.

Anyway, Mom is afraid if she dies and leaves my brother half her estate, and then he passes on, his ex might get her hands on all my Mom's money via her children (Mom's grandchildren). Mom wants my brother to get a will done so her money will go to his children when they are older so there is less chance of his ex getting any. This has been going on for three years since his divorce, and Mom tried to pressure him by telling him she will not leave him anything if he has no will, so he tells her to give it away, but he still does not have a will, and Mom still didn't write him out of it. I do not want to tell mom to leave everything to me because it will sound like I want all her money for myself, but I don't, I just don't want the ex do get it and do whatever she wants with it and not give it to the kids.