I would tell family who want extra day that you cannot accomodate their request. LEgally you have limit and there is no capacity at moment to fullfill their request. Chances are they will go if they really need extra day anyway. That take care of that issue.

Then tell remaining PT family that you have decided to switch to full time care only. That PT is very hard to schedule and means either you losing income from empty day or losing client when needs change. That the regs have hands tied and you need to make this business successful. Offer them first refusal to extend days and absorb empty place from family that left or let them have notice for the change to full time clients.