I do this every year (under normal circumstances) as someone without children.
It works fine. The holiday isn't based around going clubbing and getting wasted - I know that and would go on holiday with friends minus their kids if it were.
Big enough accomodation is key. Decent grounds/garden so the kids can roam around.
Usually parents alternate getting up in the morning, the resting parent and child free adults turn up later for breakfast then. No requirement for all meals to be together!
The kids mess about together with parents taking turns to keep an eye on them. With a big garden/pool/outdoor toys etc plus having a bunch of kids to play with, they seem delighted and so tend to just stay there all day playing/swimming/scooting etc. We don't really take them out on activities beyond a picnic in the woods near the house with teddies etc.
Childfree adults and parents not on duty might go for a walk/bike ride/excursion etc.
Usually I and the other child free adults marshall the kids for a few hours at some point so parents can have a lunch date/walk/etc together because I like my friends and it is a nice treat for them (i quite like their kids in manageable doses as well)
The only hard and fast rule we agreed on was the kids go to bed at a certain time. It may mean one parent is upstairs attempting to force them to sleep for a while but it means all adults know when the kids are expected to be gone.
And then it means we have a few hours of chatting, dinner, catching up etc without small people. I don't expect 24 hours a day of undivided attention from my parent friends - 3 hours is a delight and helps maintain our friendships.
The important bit to harmony is that both parents pull their weight. The tension if one of them does not is palpable.
So yeah if they want to get wasted all the time, just send the lads off on a child free weekend. But holidays as a group can work if everyone is a grown up about it and realistic