We've been taking along friends of our kids on our timeshare vacations for several years. When they reached ~14-15 years old, we started taking their friends, for only short stays at first, 3 days or so. Before letting the kids make an offer, we told them the ground rules. We'd provide ground transportation, lodging and groceries for in-room meals. Sightseeing, food bought out and souvies were at their and their friends' own expense.
They and their friends were expected to be
extra considerate of siblings and siblings' guests, understanding that a larger crowd results in more complicated socializing. There would be NO disrespect toward us nor of our rules. Everyone had to be in the condo by age-approp curfew unless they were with us, parents. Quiet time (no tvs, music, cell calls, etc.) was between 1AM and 8AM. No going off alone nor ditching anyone alone and each group had to call us on cell phones whenever plans changed to keep us informed or ask permission in advance. Everyone must shower daily, use deodorant, keep their own possessions out of everyone else's ways, hang up their own wet swimsuits, keep track of their own bath towels and put their own dishes into the dishwasher. After chaperoning several youth camp trips with our church, we knew which rules needed to be spelled out in advance and these were them!
Not once in 6 years did we have a problem with a young guest that could not be handled with a brief and simple reminder. It wasn't long before friends were coming along for full week trips. Our kids only invited friends that they knew they'd enjoy with this much togetherness, and who they knew would not have a problem with house rules. They have been great guests, most very, very flexible. Several have surprised us by how much they seemed to enjoy family time, with an evening of group board games and an in-room movie night. We've given them a fair amount of freedom to spend time on their own so they did spend a little less time with us but we still enjoyed the closeness of our family. I think it's worth trying for some trips.
BTW, ILoveMyDVC, DH and I met at a campground in your town, Hope Valley, RI, in 1977. It was called Whispering Pines. There was a nice little bake shop out at the main road, where my father went each day to get the newspaper and some pastries for breakfast. We were both from other states.
What great memories of our first meeting that weekend.... chatting in the lifeguard chair with a full moon above the lil' swimmin' hole.
We later added a couple nights of camping there to the end of our honeymoon too.