Bloody hell Emily .... despite the sensible advice about wills and insurance I don't think the main issue here is ignorance of practicalities but about his appalling attitude towards you and DS.
It would have been entirely different had he said "I don't know what to do for the best in the event of my death - I/we need to find out all the possibilities so that all my kids are adequately protected". Instead, he's said he wants you out and seems not to care. Social housing indeed - does he ever read the news these days - no-one can rely on being given social housing and why the heck should you depend on that as your "insurance policy" anyway ?
Without meaning to be (too) rude I'm going to suppose for a moment that he's rather thick and hasn't heard about life insurance - though I find that hard to imagine really. So .... he thinks the only way for his older kids to get their inheritance is to have you sell the house. Any normal person would have been distressed at this scenario, as in, "oh dear, I don't know how this is going to work, if my older kids get their inheritance that means you and DS lose your home, I can't see any way round that" ..... at which point, you step in, and say "don't worry, there must be a way round it, let's get some legal advice" or even (!!) "actually, there's this marvellous thing called life insurance ..... "
BUT ..... he's not expressed any concern for you and DS .... in fact it comes across from your posts that he couldn't care less hence the flippant social housing remark.
And have just looked back and seen that he suggested YOU should get insurance if you're "that worried" so not only has he heard of the insurance concept, HE isn't bothered about his youngest child and has dismissed your worries by placing all the responsibility for minimising future risk onto you. Good god.
This sort of thing is something couples do TOGETHER when they have children. It's not about one parent opting out of their responsibility to their child (or one of them). Indeed, if he thinks it's the responsibility of the mother to think about the future should he die, then why isn't he asking his ex to make similar arrangements if she's "that worried" ? Why is he going to the effort of making arrangements (which are crap, divisive, unfair, and extremely hurtful) to make sure his older kids are okay but in effect saying his youngest can take his chances ? He has every bit as much duty of care towards the youngest - and should be seeking solutions which are fair for everyone. It beggars belief that he's happy with a scenario where you lose your home so that the kids who already have a home can get a cash lump sum too. Even in the extremely unlikely event of you getting a council home, does he not imagine how stressful the whole process would be for you and DS - selling a home you feel safe and secure in, scraping about for a council property (which you'd have very little control over) or private rented where prospective tenants on housing benefit are barred from so many properties anyway, so you end up in a dump as that's all you can get. Does he really think a scenario like that is what a grieving widow should have to cope with when it could so easily be avoided ?
Yes ... all of this could be sorted out practically with insurance and trusts. But what about his nasty callous attitude ? Why the concern for some of his kids but not all ? I don't think I could forget this in a hurry.