I'm glad to hear that you are seriously contemplating going the raw food route.A vet that I was using years ago turned me in that direction due to a kitten's compromised immune system from stress, and other factors. Where conventional drugs wouldn't work we had to use alternative meds and raw food to overcome the problems.
I see L4H recommended catinfo.org and my personal feelings is that it is one of the better websites for cat information, and it's a very good spot to start. I could suggest a couple other sites but it would just be confusing the situation. Pretty well everything you need to know is on this site to get started.
After reading your Post a couple of times it would appear to me that the cats are suffering from stress big time. I would expect that the breeder had the kittens into the vet before you got a hold of them for their vaccines. Had they been neutered? Then you pick them up, put them in a new home, changed their food, had them to the vets, got a second kitten, as you can see the list goes on, and for an animal that really doesn't like change there was a fair amount of it.
Was there an introduction period for the new kitten, even though they are from the same breeder just different litters. They would still be strangers even though a short period of time between bringing each one home. It's like a new cat to the first one.
I can sympathize with you because I did almost the same thing, part of the reason for raw feeding in our house.One of the side effects from this was extremely loose bowels mixed with mucosa. It was that bad that the vet even suggested using Pepto-Bismol to treat the problem "bad idea" cats hate the taste. If you are unable to get the bowels under control in a few days send me a private message and I can give you some suggestions you might want to look at.
The meats that are being offered are by far much better than dried or canned. We have fed all of the meats to our tribe, but their favourite is pork because it's a milder meat. I'd need to have the web site for the food so I can check it out for nutritional value.
There could be a small difference between the dog and cat food, but it would likely be minimal so it would be a start for you.