My brother and I are currently sharing a house. It's pretty big, having five bedrooms and two baths, and it's been working out fairly marvelously! I have one kid, 16,and he has shared custody of his two daughters, ages 11 and 13.
His kids are great kids, but they do a few things that drive me up a wall. The main thing is the length of their baths. We all mostly use the upstairs bathroom,as the one downstairs is super small, and in a weird quirk of the home, the shower part, (no tub), is across a small separate hall from the actual bathroom. The upstairs bathroom is large and airy, and as my bedroom is up there, too, I prefer the convenience rather then the downstairs.
It's normally fine, but my nieces are in the habit of taking two-hour-long baths. They play with a bucket of Barbies, read, etc., and just take their good old time, one after the other. It gets super frustrating, waiting for them to be done, so I can grab a quick shower. I never say anything, as it's nowhere near close to a hill to die on, but still, it can be annoying. They also don't use a mat or towel to step on and thus get water all over the floor, and they make messes in there they don't clean up. I give it a thorough cleaning once a week, and I'm tired of having to move a stack of books back into their bedroom or stepping on Barbies!