Suppose that Team 1 has players Adam and Bob. Adam takes a double minor penalty, and during the powerplay, Bob takes a 2 minute minor. Then, on the 5-on-3 powerplay, Team 2 scores a goal. Assuming that Adam still has more than 2 minutes left on his penalty, does Bob come out of the box, moving to a 5-on-4 powerplay for the duration of Adam's penalty, or does Adam's penalty time get reduced to 2 minutes, and the 5-on-3 continues?
Suppose that Team 1 has players Adam, Bob, and Chuck. Adams takes a 2 minute minor, then Bob takes a 2 minute minor during that penalty, and then during the 5-on-3, Chuck takes another 2 minute minor. Now, I believe that it's the case that Team 1 plays 5-on-3, but Chuck's penalty time doesn't start until Adam's is finished. Also, assuming that there's no stoppage in play, when Adam's time is finished, he doesn't immediately exit the box. However, if Bob's penalty time also finishes before a stoppage in play, then Adam comes out of the box to bring Team 1 to 5-on-4? Furthermore, if there is still no stoppage in play, and Chuck's penalty time finishes, then Bob comes out of the box putting both teams at even strength, and then Chuck comes out at the next stoppage in play? Also, how might things change if Adam or Bob had a major penalty?
Suppose that we have Adam and Bob on Team 1 and Zack on Team 2. Adam and Zack take offsetting 2 minute minors, and while play is 4-on-4, Bob takes a penalty, but Team 2 scores before Team 1 can touch the puck. Does Adam come out of the box and Bob goes in, with 4-on-4 continuing until Zack comes out of the box, or does Adam stay in the box, and Bob doesn't go to the box?
In situation 3, the goal washes out Bob's penalty, teams remain 4 on 4.
I believe in situation 1, the way the NHL rule is written, Adam's time above 2 minutes should expire and the 5 on 3 continue, but I'm not sure this is what they would actually follow. Rule 16.2
In situation 2, the NHL rule is that none of the players in box can be released until a stoppage in play occurs (unless the team is entitled to 5 players on the ice), even if their penalties are up. Again, I'm not sure they would follow this to the letter. See Rule 26.2