Most vets won't spay/neuter cats until they're 6 months.
I got a stray pregnant cat this spring. Came with the place I moved into. :/
She had 5 kittens. Taking my cat count up to 8. My 2 original cats had both been fixed, but there's no way I could afford to fix the 3 females and 3 males. I can't even afford to get mama cat fixed.
I told the people who were taking the kittens that they had not been to the vet yet. As long as they know, then it's fine from my perspective.
I don't know what the actual rules are, but it's either get them in to homes or send them to the SPCA where they may or may not find a home. IF they're even willing to take them from me. I called the SPCA, after I'd found a home for 2 kittens. They said they wouldn't take any of them unless I surrendered all the kittens.
I was supposedly put on a waiting list for a reduced rate for fixing them, but when I called back a month later they asked if I had given my yearly income. They said they would have someone call me back to get my information.........
I've pretty well given up on getting them fixed anytime soon.