I'd certainly be asking for proof of ownership when they do turn up, Ron, like an adoption certificate or microchip details?
At least give the owners a grilling about how reluctant you are to release these kittens to someone who has left them to die in a bathroom
Oh, and do make sure they pay a hefty bill for Boarding Kennel Fees for the length of time they are with you, yes
after all, it's not your fault they were left to die and had to be rescued, why should you foot the bill for their rehab ? Maybe they'll be more careful next time.