Question: Is it right to be upset by this?
My parents are splitting up (I'm 15), and my Mother has told my Dad that he can have custody of my brother, one of my sisters and I, as long as she gets custody of my other sister. It's obvious that she favours that sister over the rest of us, but I thought that as our mother, she would at least put up a fight for us. But she hasn't. In fact, she doesn't even seem interested in being part of our lives anymore, as long as she has our sister.
Is it right that I'm upset by this?
i'm sorry that your mom is being like that. yes, you have every right to be upset. the easy answer is to tell you to be appreciative of your dad, who DOES want you. but to say forget about your mom doesn't work as easily. have you talked to your mom about it at all? tell her openly how it makes you feel. if she listens, then good for her. if she doesn't, then you will know that you need to take care of yourself and move on from her.
Of course you are right. If this is the way things happened, I'm surprised that your mom has been so obviously favoring your sister.
Hopefully your dad is a better parent. I wish you luck.