Hi
I suggest you have a look at some of the hire boat websites to get an idea of how they fit in the number of berths you would need.Then have a think about storage space for everyone and think about how small a boat kitchen is ,it can be hard to cope with 4 never mind 7.Ask yourself where is everyone going to sit in the evening and how are your children ,all at very different stages of life .going to be able to have any space of their own. How are you gong to sit down for meals and how big a table do you need so everyone can do their school work ? I speak from experience when I say that if someone is trying to work then everyone else has to be quiet -sound travels in a boat.This is not so bad for us as there are only 2 of us but 6 other people ? The water tank would have to be very large or you could end up filling it every day.How are you going to do the washing and dry it. Remember all the fuel,food and other supplies have to be transported to the boat ,this can be a challenge in a marina and much harder if you CC . You would probably have to have a pumpout which would still need emptying regularly with the associated cost.Living on a boat has challenges which I feel increase in direct proportion to the number of people on the boat .