Is it unfair of me to give my mom this ultimatum for her own sake (warning - long question?

Your mother is extremely self-centered! I myself have battled with depression and have taken anti depressants. Yes weight gain is possible, but this is secondary your mom needs to do whatever she has to do to get her life together for the sake of her children! You and your siblings are her first priority! I think you should stay in The US with your grandparents and feel no guilt whatsoever!!!! Your parents are the ones at fault, both of them. I am sorry that your private school closed, It was probably your sanctuary. Take care and remember, if you go back to Australia, you will most likely only be enabling your mother to continue the path she has been on.