I tried a number of methods.
1. Golden Malrin dissolved in a can of coke. Quick death. Just make sure your cats don't drink it.
But it never worked for me - I left some out there, but they puked it up before it had a chance to kill them. I had to lock the cats inside during that time which was annoying.
2. Shoot them. I left some cat food out in a certain spot for a few nights until they were used to coming for it. I then got the lawn chair and the .22.
I got one who died quick. Another died slow, and only after he crawled into a building on my property and hid. Died there, rotted and stunk to high heaven. That was nasty until I managed to find him, all goopy and covered in flies.
A third one I grazed the top of his head - gave him a reverse mohawk. He never did die, but my FIL caught him in a live trap.
3. Live trap. I managed to catch a few more in the live trap and released them a couple miles away. Never saw them again. I guess this was the easiest for me. I didn't have to sit out there or manage the cats. Just set the trap with cat food and check it in the morning. I caught my own cat a couple times, but that wasn't a big deal.
I managed to catch an annoying neighborhood cat with a live trap and relocated him about 10 miles away. But the commercial live trap didn't work, since the trigger for these is rather stiff. I made my own box trap with a figure 4 trigger. That worked great. That stupid cat would come into my house (cat door) and meow outside my bedroom door. That was annoying enough, but when he started spraying, I began the war.
Good luck and keep us posted.