ARGH PLEASE HELP ME!!!!!!!!! :L

My best friend is amazing and i love her so so so much, she's like a sister to me, and we are so unbelievably close. I also have a second best friend. We arent as close but ive known her since i was like 4. But my best friend has made friends with these 2 girls from my primary school (E and D) who i used to be friends with. They're ok, but they piss me off sometimes tbh :P My second best friend used to be friends with them but they supposedly called her anorexic and left her out and stuff so she left them and went off with the 'popular crowd' who have now ditched her. So she's stuck by herself and she's also really lonely and depressed because her mum verbally abuses her (im the only person who knows this) and she thinks she's ugly and stupid and all this stuff that she's not. I try and tell her but she wont listen.
my best friend doesn't like her anymore because of a rumour that E and D told her. Im stuck in the middle of my two best friends and it's SO awkward, and Im so confused on what i should do!!!! which one is in the right????
Suggestions would be appreciated please, im rubbish at this kinda stuff ;) xxx