I agree with Leed - in order for things to change you need to find a way to speak up, your mother must know of what happened with your father, tell her that you're not interested in whether or not she believes you - it is the truth whether she likes it or not. I think its important that you explain to your therapist that only you know how you feel and you are happy to explain if you know you are going to be taken seriously and listened too - otherwise whats the point? I think therapy will be a good oppertunity for you to explore how you and your family members relate to each other. As for your sister, as soon as she starts her torrent of verbal diarrhoea i would state calmly but firmly that you are going to disengage with her now because unless she can speak kindly to you you're not interested in what she has to say. From there leave the room and focus on you and what you want to do.

In terms of your diagnosis - that is a lot to deal with at such a young age. Im suprised you've been diagnosed as borderline, i have the condition myself and was told you cannot be diagnosed until you are an adult. Im not saying your diagnosis is wrong but i would make sure they are dealing with the symptoms you experience regardless of what they're grouped together and called. Really give therapy all you've got - if the situation from there doesn't improve at least you would have given it your best. Would going into a group home really be such a bad idea? Get as much information on treatment options as you can - will you be given frequent, good quality therapy at this group home? If things at home continue to deteriorate perhaps having a break from the situation and focusing on you is the best option. Remember, you cannot change your family but you can change how you react to them and improve your chances of getting the most out of life. Whatever happens i wish you the best. Good luck.