Make sure the women's watch is quartz.
Do you think they would get offended by getting replicas? Some may take this the wrong way.
Age group?
I can't think of any particular "his and hers" set, aside from something at a Wal-Mart.
If you already know they are interested in replicas, for guys, hey, anything probably goes. Breitling Avengers are pretty much universally admired.
Bigger watches are "in" for women... my wife likes the Michael Kors watches. I bought her two gen Rolexes and a Tudor, and she refused to wear any of them and got a Michael Kors watch.
Fossil seems to be popular with men and women, and since they make the Michael Kors watches anyway but have a huge selection of men's watches, maybe you could go that route.
For ladies rep, maybe that Chanel J12 or a Cartier Tank.
I don't think I'd get anyone a Rolex rep unless they specifically asked for it.