@Astrid The Battery Eater well, yes. They are, just differently. Some alters may have a full life in only the innerworld! Almost anything that's possible in real life can occur in the innerworld. However, alters that front fairly frequently can also have a somewhat full life outside of the innerworld, in the real world.
@Lovenderr our innerworld is as of yet fairly undeveloped but still kind of large for the system size. We've got a main room which is pretty small, with beanbags, a desk, a window seat, etc. From the main room it leads off to two bedrooms. My own and Ori and ace's. If you walk out of the main room there's a huge kind of basketball court size room which we use to have nerf fights sometimes (ajdbbdbd and other things). Off that room are a bunch of doors- lukas's room, armistice's room, the door to the forest, the map room and the kitchen. The forest is ace's favourite space. It's pretty huge and near the end of the forest is a replica of my old house, which I often feel homesick for so I visit it sometimes. That's pretty much it!
@Adorable almond basically the answer is no, not all systems can. For example, I can't communicate well with all of my alters. The alter I talk to the most easily is Lukas, but the rest I find hard to hear. Usually when an alter is co-con I can somewhat feel what they want to do/their emotions.