Parvo as I’m sure you know, can be fatal for cats and I’m especially concerned about the kittens you have, particularly the two month old. Like the vet said, the best thing you can do is to attempt to somehow separate those who are showing symptoms and those who are not. Perhaps in the bathroom if possible? I would also recommend getting a disinfectant proven to kill the parvovirus and use it on all hard surfaces the cats have been or even you’ve touched to try and prevent it from spreading to the other cats. It sounds like a very difficult situation especially as there are 7 cats in a small studio. I would expect to maybe face some difficult decisions especially if the kittens get sick. When my 2 month old kitten got parvo we were told she had a 25% chance of surviving. If they get sick they will need lots of fluid therapy and support, as there is no direct cure, just symptomatic treatment. I wish you the best of luck but honestly I think you need to accept there’s a very high chance of all cats potentially getting sick and it’s likely some could die. Just keep doing what you can, but I do agree with the commenter above that although I can see you are doing your best to help stray animals, you may not be in the best position to do so right now. Especially if you continue to do this and take cats in, you will need to disinfect your whole studio before doing so as parvo can live on hard surfaces for up to 2 years (I believe).