@WouldIwasShookspeared
I'm not sure we can talk about what's morally right when we're talking about a man who bought a house in someone else's name because she had right to buy the house from the council with a huge discount and he didn't.
I am not a lawyer, but what I'm seeing here is this.
A lives in a council house for a long time. A doesn't have the money to exercise the right to buy.
B and A begin a relationship. B has enough cash to give or lend A the money she needs to buy her house, and they agree he will do that. We don't know the terms because OP and her family don't have the paperwork, if there was any.
A buys her house, using the money from B. A can't put B's name on the deeds, even if she wants to, at this point, because she would lose her discount. Where the money comes from is surely irrelevant to whether she gets the discount. Most people would have to borrow it from a bank or building society.
After three years, A could transfer the property into joint names without having to pay the discount back, but she doesn't do that. We don't know why.
She could also have married B, in which case if she didn't make a will he'd have got the first £270k of her estate and all personal items. But she didn't.
She could have made a will leaving him the house or a specific sum of money, but she didn't.
She (and he) may very well not have understood that he would get nothing at all without a will or a marriage. Lots of people assume that if they live with another person they will be treated as if they were married.
However, as things stand, she has died intestate and unless B can produce documentation that makes it clear she owed him the money her estate (house + ??) will pass to her children. The fact that he is living in the house might be relevant. I think there's a law that says dependents ought to be provided for out of fairness. However, that's for a lawyer to explain, and I have no idea whether his particular circumstances would mean he qualified as a dependant.
OP, or rather her husband, really needs to see a lawyer.