Putting their cages next to each other is an excellent idea, they will call to each other through the cage bars. I would give them a couple of days, then introduce the birds together. Just make sure you have enough perches in the cage so they won't feel crowded.
Also a good time to do it would be right before you feed them.
The way to tell if they are male or female is to look at the color of their cere. That is the part right above the beak that looks like nostrils. If it is pale to dark blue they are males, if light tan to brown they are hens. Males usually don't squabble much with each other unless there is a hen or two in the cage with them.
Hens can be very viscious at times, they have a tendency to hold on like a pit bull when they bite. Males will just make a pinching bite and release, but they will do it repeatedly.