I just need to vent! Long..

My SO and I decided we were moving in together this week, we were going to move into his parents house because we wanted to save money so we could get a house in the next year or two. We told our parents brothers and sisters about three weeks ago and they all agreed and supported our decision, a week after we told them his sister and her husband decide they want to do the same thing and move back to my in laws house knowing we were going to move there in two weeks!! I was so pissed off! They already had a house but decided they wanted something bigger and let go of the other house they had been paying for, now I come to find out she might be pregnant with #3 which means they're going to stay there way longer than we were!!! Now we don't know what to do, I can't even stay in my room because my mom agreed to let my aunt stay there so I'm living in the couch of my own house. My boyfriend litteraly has his bed in a corner of their living room because his sister and her little family took his room. I'm beyond pissed and hurt, they knew we had plans, we had both put money into that one room so we could be really comfortable since we were going to stay there for a while, we came to an agreement on bills with his parents, everything was going perfect. I just hate people that want to be on top all the time. I'm so annoyed I don't want to deal with this the rest of my life and it's interfering with my relationship with my SO