I think the point of these videos is a "proof of concept" that simple/off-grid living is possible. Most that do it, don't have large families, but that doesn't mean it wouldn't work for large families. Just build the house bigger, make the solar bigger, make the hydroelectric system bigger.
The issue is one would have to start a project with future growth of family in mind. That's easier said than done.
The main problem is the banking/construction industries aren't set up to loan/build these kinds of properties. But it's definitely possible, with planning.