Answer:
One CTR with one conductor on behalf of another (checking box 2b) and three individuals with box 2c (person on whose behalf transaction was conducted) OR, if the conductor was the payee of one of the checks, change the conductor's check box to box 2a (on own behalf) and used box 2c for the other TWO payees.
This all assumes that the checks are being cashed on behalf of the payees. If that isn't the case, the CTR would look different.