((((LMo))))
I feel for you. I am sorry your father put YOU in that position, it isn't fair to you. If he wanted to take care of your stepmom, he should have done stuff on his own, not put you in this position.

I do think you compare her relationship with her own kids as something negative against you. It seems like you expect something from her that she is unable to give you right now. There is nothing wrong with her wanting to be near her own children, it doesn't mean she doesn't want to be near you.

Have you told her how hurt you feel? I wouldn't let your jealously ruin a good thingk your kids could have with her as a grandma. I saw one grandma only once a year, and I was closer to her than my grandma who lived across town. I even named my daughter after her.
45 mins is really not that big of a deal. My step kids live at least that far from me up to two hours, and we still have a good relationship with them. It isn't that big of a deal unless you make it own. There may be many reasons she wants to move out of town, and it may have nothing to do with her liking one sibling over another. Her other son lives near you, does he feel like his mom is abandoning him also?
Are you in therapy or can you talk to someone objective in this manner.
But I can understand her hurt if she cancels her plan with you to be with them. Have you told her how much it hurts you? I am sorry if I am saying the wrong things, I don't know your whole story.