<human>: Can you succinctly summarize the text in 1-3 sentences?

My parents have divorced ages ago. It was a hard time, but looking back at it now, I feel like I've become a stronger person afterwards. I lived with my mum and 2 sisters (one older, one younger) for a few years and went to my dad almost every weekend. Both parents found a new partner and got married again. They still are. 
Now here it comes..  My stepmother is great, she already had two daugters from a previous wedding and they're about my age (and my sisters) and we got along from the first moment.
My stepfather hadn't been married, never had kids. So he was used to being alone. Still, he chose for me and my sisters too when he married to my mother. The first year was great. We played tennis together etc. Then, he and my mum decided to have more kids. 2 of them..
2 more girls came along. Ever since that moment, me and my sisters started to feel unwelcome in the family. My mum did not make any difference between her kids, but my stepfather always has.
Two years ago, my youngest (real) sister decided to move out to my dad. My mum was heartbroken, but the relationship between my sister and my stepfather didn't work.  Now, we have come to a point where my oldest sister wants to move out too. And I have no idea what to do. Moving out too would totally break my mum, but staying in this place being unwanted might break me..
<bot>: Stepfather doesn't want me (or my sisters) both of the sisters have moved out or will move out soon. I don't know what to do.