I can understand not wanting to have to drive two vehicles everywhere you go. With a bus conversion you would be able to tow a vehicle which would allow you a different vehicle to use while the "house" is set up.
With so many people along for the ride you are going to have to get very creative in how you set up the living arrangements. What works on a warm sunny day most probably won't work nearly as well on a cold rainy day.
There have been a few builds on here that have come up with some really neat ideas to transform sleeping spaces at night into living spaces during the day.
Regardless of how you lay things out you are going to have to design and build some sort of bunk bed arrangement. Even if you raise the roof two feet you are still going to have some pretty tight sleeping arrangements.
There is a company that has been doing just that for more than sixty years. They run their rigs all over the world and get a lot of repeat customers. So their arrangements must work for people. Each of their sleeping pods are 6x6x3.
You can see a few of their rigs here: https://www.uniqhotels.com/rotel-german-bus-hotel
The most important thing you need to find is a bus with the biggest HP engine and high speed rear gearing. It is much less expensive to purchase a bus with those spe'c's than to "fix" it later.