Cats keep spraying how to make them stop?

you can spray the area they use with No More Marking. You can put tinfoil on the areas they spray (works for houseplants). You can get the males fixed (you did that). You can separate them all (this is a territorial/I'm mad at you phenomenon). You can take them to the vet to investigate urinary stone/crystal formation (some cats pee all over because of this and it's treatable).

To make an indoor cat an outdoor cat, start taking the cat out onto the porch when it is raining or very nasty outside or just before feeding time (so they want to come back in). Take them outside and sit and pet them on a chair or step. Leave them for 10-15 min and then call them back to the house and feed them, pet and groom them, when they return. Then start extending the time. Only cats with claws should be outdoor cats in my opinion.

If you have male cats then they spray for many reasons. Normally when they are fixed they will not spray things unless they have an infection. Male cats tend to hold their urine for as long as they can and then they develop a infection because of it. Our male did this and ended up having a very bad infection. This is what the vet told us about our male cat. You probably need to get your cat to the vet to get checked out. If you plan on putting them outside then they should be checked out before you do. If they are de-clawed then you should not put them out for any reason since they could not defend their self. Most male cats roam and may be gone for long periods of time.

Yes the cats will be fine if you put them outside just put them out there and feed them they like to explore and they will