i think with any pairing (two males, two females, male and female), you have the same problem. they may get on, they may not. they may get on quicker, sometimes it takes time. chinchi and fluffy took two months to bond and until the last week it looked like they would never get on, they wanted to kill each other every time they saw each other. just last week, i managed to get my rescue girl live with one of my boys (he's neutered) - we started the introductions in april. apparently, two adults are harder to bond than an adult and a kit.
however, i'm wondering, if you don't have chins yet but are getting two, why not get two girls or two boys from the same litter? they will already be housed together and get on, there's always a chance they will have a change of heart sometime later as that apparently happens but that can obviously happen to any pair. i think this would be the best solution for you.