LW, it feels like you're borrowing trouble here. It doesn't sound like Grandpa is on the cusp of kicking the bucket, so if you're thinking about living together now, you're going to be looking for somewhere else anyway. By the time the inheritance comes into play, the parents and brother might have moved out or moved on anyway. Use that time to figure out if you do want to live with your partner, and find a place worth making into a long-term home that you live together in, and work on selling them on the idea that it's nice to have your own place where you don't have family in your pockets (your partner can spend the time pointing out how nice it would've been if you'd had family nearby every time there's a minor crisis.) Hopefully Grandpa lives a good long time and doesn't expect your partner to put his life on pause until he inherits.