I had to share a room with my brother (2 years younger than me) til I was 15
We actually lived in a three bedroom house, but the third room was chock full of my dad's books, to the point where you could only just open the door. As was the front room downstairs, although my mum was desperate for a dining room, and threatened divorce over the book issue - they were EVERYWHERE, all over the house, but had completely taken over every room that wasn't in immediate use.
So don't let your kids share as littluns if you think their dad might turn out to be a hoarder - they may never get their own rooms!
Seriously though, can't you stay put and just get window locks and maybe a panic alarm or baby listener in the kids' rooms? I doubt the nasty thing you described is common, especially as sleeping downstairs is generally considered safe where you are? Just my thoughts, but it's what you think is important, of course.