Aha I found the pictures! So it's more HDTV treehouse than a 14 year old's tree fort. It came about before Allura was in game so my general rule of thumb is "make up whatever makes it more fun/makes sense". Allura definitely has her own room because she's not about that life.

Alternatively, Allura presumably still has her apartment in Olympia so they could all just collectively live out of both places.