"Teachers decide who is on school council. No vote by pupils, no teaching of democracy or British values."
I don't believe that. There would be an outcry from all of the parents of keen kids who didn't get a go. There will be some mechanism for being appointed, you just don't know what it is. Why not ask instead of grumbling away?
"The school parliament have been told about staggered openings for schools before parents have."
This is common knowledge, in government guidance and all over the media. I am sure that they were not given state secrets.
For all you know, someone asked what time school would start on 1st June and the teacher - going above and beyond by conducting a council meeting via zoom by the way - replied that it was probably going to be staggered.
"I personally don't think heads should have favourites or if they do, it shouldn't be obvious! "
Again, how do you know the Head isn't sending the same info out to any child who contacts her or sends her work?
I think you sound paranoid and ridiculous. All schools have their poisonous grumblers - misinterpreting gossip, spreading misinformation, thinking they know stuff 'for definite' when they don't.
If your child wants a reply from the Head, send her a piece of work and a nice, supportive message.
If your child wants to be on the council, ask what she can do to make that happen.
If you're not happy with the way council is run, just first clarify that you are correct and ask about the points that bother you.