Blackjack Tournament Question

[MichaelOar]

Last hand of the round. 3 players advance:

P2--35k, bets 25k (maximum bet)
P3--40k, bets 20k
P4--35k, bets $500
P1--40.5k, is last to act, bets $500.

P4 is Blair Rodman. I'm P1.

My question is: How much should P3 have bet and why?

Incidentally, should I (P1) have bet more on the last hand?

Thanks,
Michael