My sister's refusal to communicate with me about our father's care has brought back to mind years of mistreatment by her. What can I do?

I just have to add another insight -- coming from the only sister (with two brothers who haven't been much help). If you want to be a "valid" member of the family, then you have to be there to help. Period. You cannot live across the pond, not talk to your family in years, and expect your opinion to matter. If you don't spend face time with your father, how can you pretend to know him? The phone doesn't give you that. If you want to participate in family decisions, you need to get your butt back home, realize it's not, "all about you" or your feelings (of invisibility or whatever), and stop blaming your sister ... who seems to be the only one taking real responsibility. Stop thinking about yourself and how you feel. Try thinking about how your Dad feels, and how your sister feels ... and get your butt home to help, even if just for a few months. (A sister who wishes her brothers would help more)

Get your butt back home and help your sister and father -- in person. There is no substitute for that (skype notwithstanding). If you have really been gone that long, then your sister does have too much on her plate to worry about your feelings. Get your butt home and help her, for however long you can take leave. Do not criticize her or second-guess her decisions, at least until you have been home long enough to help in a real way. Let her know you appreciate the fact that she has assumed responsibility the whole time you've been gone, and that you have come back to help her now. Your Dad needs both of you to agree on things, so please let your "all about me; I'm invisible," stuff go, and help your sister and father. Good luck, and prayers with you.