There is also something in between Class B & C, called the B+, also as an option.
Or a Class A.
If you have always lived in a traditional house, there is going to be a period of adjustment, even if you moved to a Class A.
No-one has mentioned it yet but if you dont need the latest & greatest & you can find a reliable unit, your upfront cost might be less than a used Class B.
Maintenance costs are going to be higher & running costs but this isn'ta 10 year deal but a six month road trip that might end up being a year or more.
The key is knowing a reputable RV mechanic with high integrity who will do a thorough examination of any Class B, B+, C models & especially an older, bigger but more livable Class A.
While the Class B & Van Life Market is hot right now, the Class A is less so.
What a wonderful time for you & your family, this experience can be pivotal in the lives of all of you & probably the best educational experience available to a 15 year old.
See you on the road ...
05 Roadtrek Versatile 190/Super Modified & Lifted with Custom Battery Box, Two 225ah Lifeline 6 Volt AGMs in Series, 250 watts Solar, Victron BMV712 Meter & Victron MTTP 100V/30A Solar Controller, Magnum MMS1012 Inverter Charger, Onan Generator, Novakool R3800 Fridge & so very much more ...