That's really cool to hear. We used to make use of the toy library in Bristol when we lived there, it was a great way to get toys the kids could play with for 2 weeks then return them when they got bored :)
I did a lot of listening to the griefcast (podcast with comedians talking about people they lost) recently which I think helped me. No idea if that's good advice and the people on it skew heavily uk centric so you might not know any of them. Good luck!
I think this was a deliberate move from the Trello team not to implement this. They were very much focussed on the "not developers" market and didn't want to implement features which were mostly only of interest to a developer audience.
It seemed to work quite well for them commercially :)
Trello don't allow any more fine grained access than this. Power-ups can request view and write access and that is about it. No way to say we only want access to the current board or etc. Or that we only want to be able to update labels/members but not add comments.
They have been talking about changing that, but I understand it is complex and never really becomes a priority