I haven't read everyone's responses, but I would take a set schedule of 3 days per week at $180 and honor this family as your FIRST family, and allow time to slowly phase them out of your program.
They were your FIRST family, and they really are not asking for much. Good business practice says that you should take care of those who take care of you.....I promise you, in time, your accomodation for them will pay you back tenfold.
