Definitely had a similar situation, but a little different. I shared a room with two of my brothers, I'm the middle child. My youngest brother doesn't count in this since he is 8 years younger than me and he didn't move into our room till he was at least 5 (can't remember for sure). My older brother and I are only 14 months apart so we were horny teenagers at the same time. We both had separate twin beds on opposite walls of the room.

We jerked off together all the time, lights on/off didn't matter. One would start and the other would join. I mean we were hard all the time so it's not difficult. As soon as our room door closed was considered fair game regardless of the time. Never touched each other or anything so never crossed a line, but it wasn't something we hid from each other. We talked about it, made up different challenges and competed with each other since we are both hella competitive.