Ok, You have to treat them all individually, its not the parents responsability to pay for there grown up house owning offspring,
after that. you have to decide if you are going to try to recover money or going to swallow loss and drop.
If you are going to legally try to demand payment, you have to go ahead and damn the consequences, if you lose all the jobs so be it.
If you are going to drop them you have to just carry on and clean the other two but be prepared to tell them (if they ask), why you no longer go to the third job.
Personnally I would just be prepared to sit it out, keep doing the payers while dropping the non payer but every time you go leave them an "account overdue " letter, no threats of court action or baliffs ,etc, they may just be going through a hard time and when they get back on there feet (earning), pay you and you are back to square one with no recriminations.