Step kids/ room sharing

Back story I have 5 step kids ranging in age from 19-7

I met them and moved in 4 years. When I first moved in, and got pregnant right away my boyfriend was living in a 2 bedroom apartment. A room for him (us) and the second room was for kids. Mainly his 4 girls and his son usually slept on the couch. Then randomly one day my boyfriend threw everything out of the kids room and made it into a room for his son. Never discussed it with me. I was about 6 months pregnant at the time. So I set my sons crib up in a corner of my room, decorated the corner as his nursery and that’s all I had to give my son. At the kids moms house, the older two girls shared a room, and the son had his own room and the youngest daughter had her own room for sleeping but shared it during the day with the youngest who was 3 at the time. Since my step son moved in with us the second oldest girl moved out of her sisters room and took over the empty bedroom. My stepson ended up moving with us when we moved into a second 2 bed apartment. So again my son got a small corner of my room and that was that. My stepson has a lot of behavioral problems which added a ton of stress to my life since my boyfriend is always at work and I had a baby at the time. My step son and my boyfriend got into a fight and my stepson had to move back to his moms. To which she kicked the 12 year old out of her room to make room for him. I had moved a couple of my sons toys into the empty room, mainly just to clean up my living room. My 12 year old asked if she could move in with us and I said she could, I’d help her decorate any everything but I didn’t want to move my sons stuff out of the room because we were discussing moving shortly anyways. She cried and told everyone I wouldn’t give her the room. My boyfriend and I were both working as servers so in May of 2020 we were both unemployed. Last year we both ended up in good jobs and this was at the time we were looking of moving out of our 2 bed. I told my boyfriend I really wanted to look for a 3 bedroom. My son was now 2 and I really wanted a room for my son. We found a 3 bedroom and it was agreed that son would get a room and my 12 year old would get the other.

So I bought all these things my son would would like and I decorated the room the room for him. Took some time to get the money together and it’s still a work in progress. It looks very much like a boys room. And since day one my youngest step daughter has complained that room looks to boyish for her. Which it’s not her room. And his day one my boyfriend has bought her pink blankets that she keeps in there and any stuffed animal she asks for to decorate the bed. I have a basket in the room that I fold and nicely keep her things in when she’s not here and Iv never said anything to her about it, just take them out when she comes over. But she’s recently started the conversation again. She came over today and I had bought my son a bean bag chair to match his room and she moped around the house that it was to boyish and she’d only sit on a princess one to which my boyfriend promised to buy her a princess one to put int the room. And tonite I asked my boyfriend who has hanging something up in our room if he could hang the pictures that had been sitting on my sons dresser for months, again they match the room. And my step daughter was talking about how ugly they were and again my boyfriend promised to let her hang princess pictures. My son had received some stickers in the theme of his room and I let him put them all over his bookcase since again they matched the room and I went in the room last night and my step daughter had put princess stickers all over the original ones. I know I’m a horrible person for fighting a seven year old. But it’s my sons room. He doesn’t have anything else or anyone else. I’m just getting super frustrated by this. I’m not even saying I’m right, I just don’t know what to do anymore