Rebecca,
I know your heart is in the right place wanting to help these and all kitties. I have 8 that I am taking care of and a dog. Last month my vet bill alone, not counting food or litter or normal expenses, was $550. That was just routine attention. No major problems. What will you do if you get the fleas and worms back? Without continual monthly medicines, which are expensive, it is very possible that they will come back, especially with the cats that go in and out. People were able to generously donate to help you out and get everyone healthy. Keeping them that way is hard. Nine cats is a HUGE undertaking. Much bigger than just providing litter and food. Believe me, I know. I would not recommend that you add to the crew that you have now. Especially with the cost of everything going up, owning pets is not going to get any more affordable in the near future.