how many adults may sleep in a sofa bed? just 1 or 2 ( if they are pretending to use it as a daily bed)?
2 :) 3 or 4 if you pile on!
If they are willing to share a bed, 2
I have a sofa bed, and I do sleep on it. Just the sofa,I don't pull it out. It's not because I don't have a regular bed, on the contrary,I have a California King Louis the Eighth bed. It is almost new and you need steps to get into it. It has fresh ironed sheets,and a very soft Goose Down Comforter with Goose Down Pillows. I don't sleep there only because (and I know this sounds silly) my husband passed away four months ago,and I am scared of ghosts. We have no children and I'm all alone so yes, I am afraid of ghosts.That is the only reason I sleep on the sofa. I'm scared to sleep in any of the back rooms.
For many years I had a really nice (thick mattress) Queen size sleeper sofa. I had house guests frequently use it and they never complained about bars in their back or any discomfort. For about a week I had three house guests share the bed quite comfortably. I think three adults can sleep comfortably in a queen size mattress. Any more would be a serious problem, especially if any of the adults are, um, heavy. Hope this helps.