Put their cages together and see how they react. If its good, wait a week or two and put them both together in an entirely new area to them both with brand new things with each of their own scent as things to help distract them. But if when you have their cages beside each other and they react badly, try the new area idea but have one of them in a small carrier. If this goes well let the carrier chin out. After a few weeks of that, try puting them into a cage with stuff that won't have their scent. Not even the cage. All you have to do is scrub one of their cages really well. And watch the very carefully. If you see even the tiniest sign or fighting, separate them. Another thing you can do is put them both in the smallest carrier possible and go for a car ride.