It is a difficult matter in Germany. I asked about living aboard in Hamburg and they told me it would be OK for a month, but problems lie in living aboard for longer.
In Germany one needs to register one's address with the local authority (it is called anmelden or getting "Meldebestaetigung"). This is law and one has 2 weeks after a change of address to complete this; and the law is indeed enforced.
The problems begin with certain addresses not being allowed for this registration, boats in marinas or elsewhere being a case in point. Thus, unlike the USA where living aboard in a marina is a matter for the marina operator to decide upon, it is not legal to do in Germany.
You might be able to have an official "Meldeadresse" somewhere on land and actually live aboard in a marina; that might work - if the marina plays along. The one in Hamburg (CITY SPORTHAFEN HAMBURG - Marina
right in the city center) was surprisingly affordable but with all the big boat traffic there will be surge and wake issues but when I sail into Europe I would like to spend a month or more there.
p.s. Home schooling is indeed illegal in Germany.