Fact is his ex kicked him out with nothing (to move OM in). Emptied all their joint accounts, savings, remortgaged the house. By the time they divorced there were no "assets", so the house was signed into her name. DH has nothing to leave, from years and years of supporting his kids and trying to cover his own rent and bills - What the ex did is nothing to do with the children whatsoever. It's good that he is supporting his children but where does he pay rent for? If you're married don't you live together in your house?
Everything we have is mine, from before we met. My house, in my name. My pension, my savings - What happens if you divorce? Would he get half of everything? Are they not now considered joint assets?
But, as several posters point out, it seems to be assumed that there will be "an inheritance" as on the surface he lives in a nice house, drives a nice car, and lives a reasonable lifestyle - I don't understand what you mean by 'on the surface' .... he either lives in a nice house, drives a nice car etc or he doesn't?
Judging on her behaviour when they split though, she would likely come after me for "their half" - Why would they do this if your husband has made provisions for them in the will? or hasn't he? I'm confused. Or do you feel that they simply wouldn't think it's enough?
If they were successful, My kids and I would lose our house, everything. And me, as a low income single parent would have no way of keeping us all. I have been as careful as I can, but she can afford expensive lawyers, I can't - This would be horrible and I can see why you're worried. I think this is something people should consider or discuss before they marry people with children from previous relationships. I'm not saying that people shouldn't marry people who have children already but definitely set out what is going to happen financially and in case of divorce/death etc
FWIW my ex is with someone else and has a child with them. His partners parents are millionaires. If they married and she had perhaps inherited millions, then he died, I wouldn't go after her for money (and my ex has never supported our child) because he doesn't work and hasn't for some time. He is also unlikely to anytime in the near future. I would feel differently if he worked and contributed to the household financially though. It's certainly made me consider OPs post a lot more.