This is a tough one for you…..
I wouldn’t take a younger child out of school, since they are in 8th grade and may have a hard catching up (I’m not against taking kids out of school if they are not going to fall behind because of it)
I wouldn‘t go on a trip, that my oldest would LOVE to go on, without her. If it was a place that she’s just ok with, then I’d go without her.
In the end, I’d have a real good conversation with your oldest about this. She may tell you to go and not worry about her (I would have at this age) or she may tell you that she’d be very sad about you leaving her out. Once you talk to her you’d be able to make a better decision. Good luck - this is a tough decision.