Hi Ian,
Recent developments certainly make you think.
These are all great questions, I see a few schools that seem to get a deal of interaction with parents, but I mostly see likes.
I am not sure if either the #IndieWeb or mastodon are ready for schools. Twitter wins for ease of use for non-technical folk.

micro.blog is, imo, a great example of how #IndieWeb and ownership can be done. I can join in from here pretty seamlessly(for free) and there is a great community where folk who pay for micro.blog hosting and independent blogs are treated equally in ‘social’ side of things.

Manton’s book on micro.blogging, its history, problems, solutions is pretty great imo.
https://book.micro.blog If you’ve not read it I think you will enjoy it.