My PIL are lovely, I've been married for 15 years so know them well although our relationship is polite and friendly rather than super-close.
We visited recently and were talking about wills - we are trying to draw up our wills, it's been to-do since we had children etc. They said they didn't have any in place and hadn't really thought about it. I was quite shocked as they're late 60s/70s and retired, MIL looked after her mum until a few years ago when she passed away.
I think they think (as we did) if you're married and just want everything to go to the other spouse you don't really need a will. I mentioned that it's a real headache if you die without one or if you both go but I didn't feel it was my place to press it as didn't want to seem money-grabbing or morbid!
They are quite financially naive so I do worry a bit (their mortgage is paid off since FIL's parents died a while ago). I honestly don't care what they leave to whom - they live modestly and I don't think have a great deal of savings - I just worry about sorting it all out should the worst happen. AIBU to suggest that DH and possibly his brother gently suggest they get it sorted out, or is it none of my business and/or will it all work itself out even if they don't have wills? My parents have done theirs.