Your shelter is spaying the kittens you want at about 8 weeks is that ok?

Yes. Eight weeks is the youngest age a kitten can be neutered/spayed. Most people wait until the cat is around 6 months old -- and personally, I did not have my young female cat spayed until she was 9 months old -- but if they want to do it now, then that's their business.

You should be glad, actually: having a cat spayed at a regular veterinary clinic can cost nearly a thousand dollars per cat!