it's cheaper to take them off and take them in to home depot or lowes. they'll rekey them for you. the down side is, you'll need someone to stay at the house while you're gone until you get back to put the locks back on.
a lot of home depots will not re-key your locks unless you buy them from them. they will do it for free or at least they use to when i worked there if you purchase them from them. otherwise it is not hard at home depot to find 3 keyed alike locksets in one box. one of my best friends is a locksmith and to hear him talk it sounds like it would be a lot cheaper to go buy them yourself.
When you buy the new locks look at the number in the top right corner. Matching numbers use the same key. Good luck. My wife and I are looking after a friends home and we are about the evict the dead beat tenets. HAPPY NEW YEAR
