Hi OP, I'm sorry to hear of your woes. It all sounds like a complete mess and no one is happy. It also sounds like the only thing stopping you from divorcing is the money issues. I expect you would keep the house and he would keep his pension, if he stopped work. And really, you have to plan for him being on a pension, anyway, since he's 68 and really anything can happen at that age, healthwise. Any extra working years at his age are an unexpected bonus and could end at any time.
So, assuming he's on a pension and you're on 29k, what would most likely happen is that he would get housing benefit, and maybe universal credit, and he would need to rent a one-bed flat, possibly in a cheaper area. You would keep the house since you paid a lot of it off and since you have two children with additional needs. You would also get universal credit, since you only earn 29k and have two dependents and wouldn't get much, if anything, from him.
Yes, you would all be worse off than now, but when you consider that the 58k salary from him is very much non-guaranteed due to age, you might soon end up without that 58k anyway - AND having to care for him!
You would be worse off, but you would all be OK, thanks to this country having a good safety net for vulnerable people like your children and their carer (you) and for seniors like your husband. And everybody would be happier. He might be in a one-bed rental, but he would have the peace and quiet that I bet he wants at his age to just read his book. And you and your children will live without his moods and temper, and you won't have the demands of being a partner, which it doesn't sound like you have time for anyway, caring for two children with no help.
It won't be easy to break up, but I think it will be an easier life afterwards.
Before you say anything to your husband, I think your very first order of business should be a solicitor and maybe also Social Services, to see what you'd each be entitled to, in terms of UC and housing benefit.
Best of luck to you. I escaped a marriage to a man with intense anger issues, and my life is a million times nicer, even if I have less money and won't be able to retire. I'd rather work until I simply can't anymore than live with a man like that again.