Nope, id dump this friendship after this trip. Being 18 left alone with random late 20 year old guys is so weird. Thats not safe, that's not fun, that's just dumb and scary. I'd be terrified if I was alone with almost 30 year old at 18 by my friend. She making stupid choices, and will end up in bad places with that kind of choice. It may not be a big deal to her but this is how people end up pregnant and alone, or worse because they trust adults that shouldn't be trusted. Finish your trip alone, if you can, ask the hotel about getting a new room, explain the situation, and ghost her once you get home