I go away with my in laws every year, but just in the UK.
I have to say, it has got harder and harder. As kids and grandparents have got older, needs have got more and more different. The grandparents now need quiet, calm, alone time, and the cousins are very different ages and have different interests. This means more clashes and more compromises.
My SIL and I have recently made improvements by insisting on some basics: two living rooms/spaces at a minimum so the grandparents have somewhere to retreat to, and enough bedrooms so children aren't in with parents so everyone sleeps better, plus the ability to have days as separate families not everyone altogether all week.
My MIL and I also influence lunch plans so we eat out occasionally rather than making packed lunch for 12 every morning 
However the last holiday was really tough, the older cousins were prioritised both in activities and timings of the day, my kids were sidelined, we were expected to pay for a lot more (all the food shopping, entry tickets for the whole group, whole group bill for meals out) but also not allowed a say in e.g. what and where we ate (as our kids aren't fussy but cousins and FIL are).
I think it can work, but you need clear boundaries and expectations up front e.g. letting them know you'll be out as a mini family for at least one day, agree who does what chores upfront (so for example we know each adult cooks twice, and we cook in pairs so we agree who wants to pair up).
I think location makes a huge difference too, as if it's a pool/beach holiday there can be a clash if some people would rather explore than chill.