So the team has been mopey about some of the performance requirements of challenge #5. That's too bad. However, for every two extra people completing a character challenge, one person of another challenge may be exempt from doing theirs. For example:

Nine people have to do the burpee challenge. That sucks.
Only six need to do the 10 mile run, but if an additional two (that's 8 total) do the run, they can bump the requirement of another character challenge down by 1.
If all else fails, do your best and perhaps a good hint about the character will suffice?