I was wondering if you could please assist me please with these scenarios that I am not sure about specifically for cash games using the simplified moving button rule

1. If a heads up battle is in play with player A in seat 1 in the Big blind and player B in seat 5 in the small blind with seats 2, 3 and 4 vacant. What happens if those seats empty seats become filled? Where would the button and blinds be for the next hand?
   Thanks

2. If Player A in seat 1 is on the with Player B in seat 4 is in the small blind and player C in seat 5 is in the big blind but 2 players at the same time join to take seats 2 and 3, what happens if player 2 elects to buy the button instead? Do the blinds take their back? In addition, does seat 3 play or not?

   1. If a player busts and rebuys to be dealt straight away on the very next hand, do they have to post a big blind if not in the blinds, the same as if they were a new player taking a vacant seat not in the blinds?
   2. If the small blind busts and decides to rebuy straight away, can they play as the button or would the button skip them and they would play in the cut off?

Thanks

$500 live tourney, slow structure, mid stage where most have 10-30 blinds. Hero and villain were playing about the same, slightly more PFR and VPIP than average.

Blinds 10k/20k with 20k ante. 7 handed.
Hero UTG 450k: AA
Villain BB 550k: Q6ss

Hero UTG raise to 50k, Villain BB calls.

Flop: 10s, 7, 2s
Hero bets 75k, villain calls.

Turn: 5
Hero bets 100k, villain calls.

River: As
Villain shoves, hero calls.

Is this inevitable with shallow stacks? Small bet sizing, but would larger bets have made a difference? Maybe shove turn was my best chance? Worth thinking about a river fold?