I have to admit, your OP scenario is SO surreal. Who would have thunk?

I guess I'm fortunate in that while my mom is not a person I want to emulate in most ways and my sister is not in agreement with my transition, I still see good qualities about them -- because I noticed when I finally was going out that I do look a lot more like them than I had thought (especially the chin area). That was sort of a revelation for me, but also just very ... odd.
I'm guessing the OP was just a dump and a vent? Was there anything else you needed to hear from someone?
Yeah, I think you do need to face up to the issues you have with your sisters as part of transitioning in a healthy way. Once we go this road, there's no hiding anymore. We spent a lot of our past hiding and running from the reality inside of us; but if we continue to run from that stuff at this stage of the game, we only really hurt ourselves. The goal is to get healthy, whole, stable, and strong; growth, unfortunately, is usually a pretty painful and uncomfortable process, especially when you're "in-between" the old self and the new better self. I think your sibling's transition can help catalyze some of this process for you.
(And yes, it might be a bitch for her to steal your thunder so to speak -- but honestly, I'd be ecstatic. Someone in my family who actually DOES understand and will be supportive? I would LOVE to have that. If you can see it as a positive, that would help you immensely.)