In my 30 foot class C which has bed space for 6 people, 8 if some of them are small children who will bunk together, we've made six short trips (2-3 weeks) with four adults, three of those with two children, toddlers at first, the last with them children age 12 or so. Four adults for any length of time was crowded in the sense of people always being in each others' way, and regular daily activities had to be carefully scheduled. It was something we could do, having grown up with a family eight in a 800 sq ft 3 bedroom - 1 bath house, moving into one larger as we expanded to ten. So how well it works is going to depend on how well this collection of people can live together in crowded conditions.
But there is another factor, that being the carrying capacity of a Class C. Every time we traveled with 3-4 adults plus children, the motorhome was overloaded by at least a few hundred pounds, mostly because of the amount of clothing and personal items each person considered necessary for 2-3 weeks survival.
What you want to do would be better done in something closer to forty feet in length, on a chassis that can handle 22,000 to 26,000 pounds (or even better, 45 feet and 36,000 to 45,000 pounds, i.e. the size of a commercial motorcoach). Most of these larger RVs are built for full-time living for two people, but there are a few family oriented models out there.