Taking care of Fearl Cats

This is Domino and Coco

Domino, Coco, & Ltl Black

Trying to trap Smoky

Not taking the bait!

I am fostering some Fearl Cats and if anyone has any hints for me please pass them along. I've tried to catch them so I could get them spayed or neutered but they are really smart and avoid the trap even with a can of Tuna inside it. I don't want them to keep breeding, so what can I do if they won't go into the trap?

They come on my backyard screened in porch and eat, sleep there at times but not always. I bought a special heated pad that keeps them warm because it is really cold here in Detroit. I change the water twice a day because it freezes, and I keep the dry cat food under a box so the snow doesn't fall on it. Other than that I don't know if I can do anything more. If you have tips please send them my way.