Hmm. Yes it might be possible until he discovers girls.
2. It depends. In a cyclone none is big enough. In reasonable weather providing it isn't raining you can have fun in a relatively small boat if you fit and can stand it for a time.
You are mixing 3 things. One a young family - size. Liveaboard. Cruising in open waters but close to land.
Generally say 40' would be fine for a small family, depending on design and how carried away you get.
Unless you have found an oil well, and depending on how long term longterm is, I wonder if you might not be better off starting with something modest where you can have fun soonish even in a 25- 30'.