You talk about stability for the children. With Brian as their father ? I don't know that the two are mutually compatible.
You are too bad
. I guess that I see it as a teacher with 35 years experience with kids. I knew some kids that had gypsy cruisers as fathers, in fact I become friend with the fathers and later with them.
Basically it will come a time where the knowledge of Brian and his wife will not be enough to school the kids. Normally that will happen at best when they reach 9th grade (it happened sooner with the kids I am talking about). Remember that at that age the kids have already 8 or 9 specialists as teachers, each one very knowledgeable at a particular area of knowledge considered important for their education, not to mention socialization.
At that times boys and girls become also more interested in each other and in variety if you know what I mean.
From that time on Brian would be forced to be on a given place almost all the year and cruise only on the school holidays. He will try to move the boat to live in different places but at that time he will meet a big resistance from the kids.
In the end the kids will meet someone is some place and want to live with him and the family will become scattered. If one of the kids wants to continue sailing, soon it will find a soul mate and he will live to live in another boat or with another person.
Off course that can run in a different direction, I was only putting Brian in my friend's shoes:
I knew him in Peniche, one of his daughters live in Madeira, other in Antwerp, other on Martinique, the wife in London and he unfortunately had already passed way and at that time sailed alone with his wive on the Caribbean. Can you imagine the difficulty in meeting with his kids or to play with the nieces, not to mention helping when it is needed?