I very much doubt that the problems you are having are due to feeding raw meat. Normal, healthy cats have NO problem whatsoever dealing w/ e.coli, salmonella, etc. Realize that e.coli is actually a perfectly normal inhabitant of ALL our guts.
Vets were trained by Hills (the Science Diet people). 'Nuff said.
Basically, vets will always blame the raw diet whenever anything goes wrong simply b/c they know nothing about it (or nutrition generally). You're not having 3 otherwise healthy cats get sick b/c of e.coli.
Sounds to me as if there's a virus (which will NOT be helped by antibiotics) going around. You can bring those in yourself. Some viruses can actually pass between humans and cats. You've had tummy viruses, I assume? There's really very little you can do other than let them run their course, and antibiotics will do nothing other than further disrupt the intestinal flora.
I would stick to bland, plain food (chicken, perhaps, NOT cooked), feed less than usual (with a dog you might fast but you really can't do that w/ a cat), and esp. if you're going to give the abios, give a probiotic (from the health food store refrigerated section, NOT Walmart or the drug store) to help repopulate the GI tract w/ good bacteria after the abios kill it all.