The one where you have to win one tag team battle against a team with higher power, do you have to win all 3 stages? Winning 2 is classed has a victory so why doesn't it award the reward by winning 2 stages against teams with higher power.
No, just one of the 3 battles has to be won against a higher power team.
Note that it's the combined power of the champs you chose for THAT part against the other team, not the total of all your champs for 3 fights against all thiers.