One partner works on a hold, while the other goes for max reps. This is not for time, but max reps. When your partner comes out of their hold, you rest. When one partner has completed therequired time for the hold, switch. Both partners will complete each hold and your score will be however many reps you have completed together for each movement.
3 minute plank hold/max pull ups
3 minute wall sit/max squats
2 minute handstand hold/max push ups
2 minute hollow hold/max sit ups