Sorry I didn't see this till now, but what K&L said is exactly right. You're going to need 4 traps. If you trap only one, the others won't go near it if you set it up again. They're very smart when it comes to that.

Try asking some of the shelters in your area if you can rent the traps. That's what I did when I trapped Sydney (now in a wonderful, loving home in upper MI). Most of them will request a deposit, but you get it back when you return the trap. And when you DO trap, use the smelliest sardines you can find (not in tomato sauce like I did once, DUH!!) They love that stuff.