I come from a family of 7. So I'll try to answer your questions in my opinion. (Im the youngest)
1. Yes. I shared a room with my sister until my oldest sibling got married. By that time, everyone was starting to move out to college so it wasn't so crowded.
2. Very much so. In different ways. MY family is kinda grouped, so like the first three kids had one childhood, next two had a little different, and the last two (which includes me) basically grew up with different parents. My parents changed their parenting methods a lot. So I played with my older siblings but in my mind, I only grew up with my immediate older sister.
3. Ummm. I mean in my fam not that much. Sure it gets tense, but it evens out in the end. No-one in my fam has lasting grudges about a fight, and besides I did mention that they have different memories than me. So I didnt really fight with my older siblings, there was no winning those, but my immediate older sister and I did have lots of fights.
So that's basically all your questions. Hope that made sense! Feel free to ask more questions if you want