NC because the details could be identifying.
DP's younger siblings both still live at home. They pay quite a lot of the bills and rent for the house (PIL contributes from his savings), but are not named on the tenancy. The council has, in the past, offered to find PIL and MIL alternative and more suitable housing; they're both struggling with the stairs and it's looking more and more likely they'll have to go for this at some point. SIL might be able to move with them as a carer, but as you now can't inherit council tenancies, when they die she wouldn't have a home. (We think she might be able to inherit the tenancy if PIL and MIL don't move, as it predates the new rules.)
SIL doesn't seem prepared for any of this. BIL has some savings and has been wanting to move into his own place for a while, but SIL won't save. She's not flashy with money, but there are things she could cut back on and won't; she also won't ask PIL and MIL to contribute more, though they could do this.
I know DP feels responsible for BIL/SIL in an older sibling kind of way, and has suggested SIL should consider moving near us when PIL die. My worry is that we'd become the automatic port of call if SIL were struggling with money. At the moment it looks as if SIL would probably inherit enough money from PIL for a decent rental deposit, but not enough to afford the sort of rent she'd need to pay for the sort of place she'd see as liveable. I am frustrated because whenever we discuss things like how much private rental is, SIL simply refuses to consider the fact that what she could afford would be a room in a shared house or a very small place, and just says 'I don't like the idea of that'. When we say 'then maybe you'd need to start saving now?' she'll say she can't seem to save.
She's not a stupid woman at all, but she's very sheltered from having lived at home all her life, and she doesn't seem to see there's a real financial worry here. DP's heart is in the right place but she is awful with money (we've just paid off the debts she had when we met). I don't know if I am borrowing trouble to be worried about this now, or if it's sensible to try to keep pushing the conversations so that maybe slowly SIL will start realising she needs to think about the future? I am worried that if she doesn't plan, we're going to end up with SIL in a panic because she's burned through any inheritance, can't find a home she likes, and expects us to solve it all.