Stray Cats Spay and Neuter and Release

My office is located at the back of a butchery - which attracts dumped, stray and feral cats and kittens with the smell. I feed these starving cats, however the amount of cats that are now coming for food is at 22. 4 of which are pregnant. I am fine paying for the food, however, I would love to get as many as I can spayed and neutered to prevent the breeding of unwanted kittens. Also there are occasional injured cats that turn up here looking for food. I would like to get vertinary care for them to save them.