DEAR AMY: I have three older half-brothers (we share a father but I have a different mother).
About a year ago, one brother threatened to expose something personal about me on Facebook. The thing that he threatened to expose wouldn't really have bothered me, but he clearly thought it would. After that, I had no contact with that brother. Recently our father had a heart attack. I was the only one of my siblings who did anything for my parents during this time. I live two hours away and I'm a full-time college student; I had to drop everything so I could be at the hospital and drive my mother back and forth. I realize that my mother is not their mother and it's my job to see to her needs, but I was infuriated that my brothers hardly did anything for our dad. I feel a lot of resentment. They don't treat me like a sister. I hate that I'm the only one who really takes care of our dad and that I'm left out of other family events. I want to pretend that it doesn't bother me, but I do feel bad. I had nothing to do with our father divorcing their mother and then marrying mine, but I feel like they blame me. I'd like to let it go, even though I feel like I've been punched in the stomach.--Invisible Sister
DEAR SISTER: If your half-brothers are substantially older than you and were raised in one household as a unit (for instance, if they lived with their mother, versus being raised along with you), then this would definitely have an impact on how they view the sibling relationship with you.
Your gender also makes a difference -- especially when it comes to caretaking. Obviously, there are exceptions, but parental caretaking duties tend to fall to women. In leaving you to take care of your father, they are treating you exactly like a sister.
Nothing will change if you don't try to communicate about it. Don't pretend this doesn't bother you. Your father should model inclusive treatment, fairness and gratitude -- and expect his sons to do the same.