AITA for not going to my sister’s wedding?

I (f19), and my older sister “Jane” is much older than me. Because of that age gap, we basically grew up in different families. I love her unconditionally, but that doesn’t always mean I trust her or feel close to her. Our family had a rocky history, and although we’ve been trying to rebuild a relationship since I started college, it’s still fragile.

Jane is having two weddings several weeks apart,  one is near home and another in a remote location during one of the busiest parts of my school year. My Mom and Dad (who is her step-dad) has already contributed around $40,000 toward these weddings, so there’s been a lot of emotional (and financial) investment already.

I can’t attend the first ceremony because I’ll be out of the country due to arragnemnt I made before they got engaged. The second ceremony I originally RSVP’d “yes” to because I really do want to support her. But planning for that trip has become complicated. The travel would be expensive, hard to arrange, and it would be right during midterms.

On top of that, things with Jane and the rest of my family have gotten worse. She’s been rude and dismissive to pretty much everyone involved. One example: for the first ceremony, she invited a ton of people but didn’t plan any kind of reception or even drinks afterward, leaving guests with nowhere to go. She only agreed to a small celebration after a huge fight with our parents. She also didn’t invite my dad to the rehearsal dinner,  even though everyone else connected to the couple is invited and said it was because it would cost to much (but she is not paying for it, her dad is), which really hurt our Mom and my Dad, especially given everything he’s done for her over the years (pay for college would be one example).

There’s a long pattern of this kind of behavior, and while I’ve tried to keep my relationship with her separate from all of that, it’s been hard. My parents sat me down, and while they didn’t forbid me from going, they very strongly encouraged me not to. They said they’d still pay for it if I insisted, but I know it would hurt them, and I feel guilty at the thought of letting them fund something that has caused them so much stress and disrespect but I cannot afford it on my own either. They have always been loving and supportive to me, and I don’t want to put myself in the middle of a situation where choosing to go feels like choosing sides.

So now I’ve told them I won’t attend the second ceremony either. I need to tell Jane, and I want to do it in person, but I’m honestly kinda scared of how she’ll react. There’s a verrrrrry long  history of her taking things out on people when she feels slighted, and I worry this might end whatever progress we’ve made, if any. So, AITA for backing out of RSVPing “yes”? And what should I say when I tell her, I am thinking of just being honest but that probably won’t go down well? Any advice?