Simply tell them that if one gets off, you're all off and the flights cancelled.
See how peer pressure works amongst the SLF and leave them to decide.
I don't have the time to be held to ransom by silly passengers.
But that's your job isn't it, to fly passengers from a to b?.
They're not hitch-hikers, they pay your salery. No passengers = No Flight = No Job. Perhaps you should go fly freight only.