many shelters/rescues have traps that you can borrow or rent for a small fee. Sometimes you just have to put down a deposit that they'll return when you bring the trap back to them.
I'd say that if the cats are strays and not truly feral, you'd have a pretty good chance of socializing them. The one that your sister lost a couple years ago is probably just scared and timid from living on its own for 2 years. He'll probably warm up to you quickly. It's hard to say with the other two not knowing their background. It is possible to socialize an adult feral (one that has never lived with people), but not very likely to happen. Often the kindest thing to do is trap, neuter and release them again.
Does this kennel of yours have shelter from the sun and weather? That would be an absolute necessity, but I'd also be a bit concerned about the cat feeling too trapped and vulnerable in an open pen outside. It just doesn't seem like a good idea to me, but I don't have any first hand experience with that sort of thing. A comfortable, quiet and enclosed space would probably be less threatening to a scared animal.