Please don't feed your cats and dogs vegan diets, or keep your cats indoors, and say anyone who gives them meat and lets them outside is not vegan.
Keeping cats indoors is no different from zoos keeping lions in enclosures. They need and want freedom and sunlight. And cats and dogs, especially cats, need meat. Any vet will agree. You can't claim to be pro-science if you think all the vets are somehow wrong. Maybe there are some cats and dogs who live a long and healthy life on a vegan diet. There may also be some cats and dogs who get beaten up every day and live a long and healthy life. But that doesn't mean it's good for them.
I get it, it's hard to know what's right. Veganism is about preventing animal deaths and suffering. And if you buy meat and let your cat outside, you're contributing to it. Yet if nobody adopts cats and dogs, they'll eventually be put down. But torturing your pet is the least vegan thing you can do. If you want a pet, but you don't want to buy meat, adopt a rabbit instead.