Good morning, Elle!
It is dark and dry here!
Hope it stays fair for the festival!
Now, 27a!
This is my stab at the parse!
I think "chosen group" is key here.
In the Bible I am fairly sure the Jews were referred to as the "chosen people", and were descended from the "Israelites".
So an "Israelite" would be a leader of "the chosen people".
I don't know how "senior member" fits in, though. Sorry!
I could well be on the wrong track, but that is as near as I can get!
in 12a, "round up" is gather.
"work" is "run", with "o" for "old" inside, and "DUP" for politicians.
19d, the "revolutionary" is Chairman "Mao", with "I" inside, "maio" and "Wed" for the day, giving "miaowed" which is a noise a "queen" would make.
A queen can be a cat.
So, that's what I have, Elle!
Hope it's a help?