Let's see, if we assume that each person takes a 2 hour watch shift, then with 5 people keeping watch everyone should get their full amount of rest.
I think it is ok to split up resting in to two time periods, as long as they are a minimum of 2 hours.
so, I have it like this:
Kaelan, Sepoto, Charles, Trebuchet, Catherine. With each of them taking 1.5 to 2 hour shifts, then the group should easily be covered from 9 pm until 7 am.