Grandma begged us to move in. Our family thinks we're taking advantage of her. What can we do?

I'm a 32-year old woman who's been going back to college for the past 5 years. My father is irresponsible and always has been. This means he was the only one of his 3 siblings who had nothing to lose when my grandparents (his parents) needed someone to move in and help. But he didn't really help out at all - he has temper-tantrums, is messy and hordish, and ever since my grandfather died 4 or so years ago, he's been ignoring my grandma. almost 3 years ago, my grandma begged me and my fiancee to move in with her - only 2 weeks before college started. We hustled to do so, because my dad was driving her insane and not taking care of her. We cared for her along with some day-time care-givers, for 2 years. Over this time, the rest of the family didn't seem to notice how much me and my partner were helping. My grandma chose me to latch onto as her "hated person" (she's always been bigoted against women anyway) and so has been telling my family all these terrible things I'm doing like "ignoring her (studying), "not cooking for her" (cooking stuff she refuses to eat out of spite) "leaving messes in the kitchen" (they're her plates that she forgets to clean up!). Turns out she began telling everyone that WE begged HER to let us move in (which was patently not true at all.) If I ever get emotionally hurt or depressed by the mean things she says, and she happens to see me crying, she tells everyone that I am acting like a baby, or having an "episode" and need counseling. Finally, this past year my fiancee and I both went to Asia to study abroad. She was very angry at this. She even went so far as to tell me that our friends should not be having a going-away party for us at all, because "nobody will go anyway"; we also overheard her (as she is deaf so speaks loudly) talking about having our stuff "thrown away" as soon as we left: though she quickly changed her story when asked about it. My grandma is in a wheelchair, has dementia and it's getting worse. My dad always made her depressed and angry with his callous disregard for her safety, and how discourteous he is to his own mother. The problem now is that my dad has gotten a girlfriend (which is good) but he's moving out to live with her. My SO and I are still overseas, and will be until Sept. Grandma has "kicked" both me and my SO "out" with my father, as well. She doesn't want anyone there. But she's 200 lbs, no muscle, and very absent-minded, easily lonely and depressed. I'm very worried about what will happen to her, but also very angry at how the family is treating us. Everyone outside the family sees how badly my dad has been and voices strongly that me and my SO were instrumental in helping my grandma the past 2 years. But even the few relatives who are now seeing the light (seeing how things fell apart as soon as we went overseas) think she'll be okay. Also I didn't mention, but my grandma is 91 years old. Should I just accept the fact that my father's irresponsibility will always color how my other family members see me? It's like they're taking "the apple doesn't fall far from the tree" literally, but I've done my best in my life to be the opposite of my dad. I feel like I've sacrificed a great deal of my life (for no pay, btw - we had to pay rent to my grandma while my dad didn't) only for my family to attack me. Ironically my SO's family loves me and is very supportive. I just don't know what to do. I feel am getting not only burn-out from care-taking, but also from the rest of my family believing the delusions my grandma tells about me. It's also going to make returning especially difficult, as we now have no real place to return to in America. When we get back, where will we go?