I haven't read all the responses, but for us:
We live in a tiny home. We have one couch and one rocking chair. I use the rocking chair mostly for nursing, so daddy also uses it when he's putting the kiddo to sleep. We are all "allowed" to use the whole house. Kids are allowed on our bed, we change where we sit for dinner, I lay down on their beds, we all cuddle on the couch. We sit on the floor a LOT!
The only off limits is jumping on furniture (kids or grown up ;) And, if anyone in our house is sitting somewhere and another person is especially tired, sick, nursing or hurt-that person, kid or adult, gets first dibs.
We are a mixed family of religious/spiritual beliefs. My dad was a "don't bother me where ever I am" type of guy and my husbands family was very flexible (as far as I know).
Nice topic, by the way!