Well for the weight gain you need to eat at least 1200 calories or your body will enter starvation mode and burn less calories. Also if you are too restricted you might binge later...

With your mom the best thing is to ask a therapist what to do---they tend to be really good at sorting relationships. I also know you have gotten good advice on how to deal with her on here.

With your dad...its not that you have to give him up but you have to have alternatives...you are much younger and at some point you will outlive him...this is one of the reasons people start dating and forming their own families later on. If you don't feel like dating start with friendships...again your therapist should have some ideas and I know we've been though some internet based options etc on here. Once you have other support although your dad will still be very important to you, you will have alternatives that can make you feel good when he isn't available...