'Sorry guys - much as I love you all, I don't want to share beds. Some of are going to be snoring, wanting to read in bed, going to the loo...we won't get a proper night's sleep. Plus if the owner finds out, they can kick us out for over occupancy.
Can we look for somewhere else? If not I'm happy to be the one to take one for the team & drop out this time 😊'.
as an alternative, is it in a location where you could find a hotel room & join in the day & evening activities?
Also, how skint is the group?
It may be that some are maxxing out their budget & can only go if the accommodation is kept as cheap as possible. If you know this is likely to be the case, you might be able to suggest that the costs are split with a cheaper rate for 3-in-a-bed or on the sofa - those wanting a cheaper break can then opt for the sardine options & those wanting a proper bed space can opt for that?
If you know that everyone can afford decent accommodation, it's likely that other group members will agree that you all need to book elsewhere.
I'd start the convo on the group chat & see what happens. The absolute worst case scenario is that everyone else says they're happy with the arrangements, & then you're no worse off - you can just say you have insomnia/a bad back/snore & drop out politely, which is what you want to do anyway.