that makes sense that they were together in the tank at the store, cuz they know it's a temporary situation. when actually set up, for sure should be kept separate. A male and female will attack each other eventually, especially when being fed.
as for the tanks, if they are only 6 months old, wouldn't keeping each one in a 55 gal tank scare the crap out of them? I have a 900 gram older BP in a 55 gal and she's got LOTS of room. Depending on how small they are, I would consider putting a solid (wood/plexy glass) divider in the tank you have, that way they can share a big heat pad also. Again, this is all assuming they are small enough.
Congrats on your new additions, i'm sure they will be very rewarding (and sometimes frustrating