you should introduce them in a place where none of them are familuar.. like a bathtub, be ready with spray bottle just in case they fight.
We were trying that and everything was working out great until we put them together in the cage and Mokey and Mushroom both decided they were the alpha rat. So we are still letting them play in the tub and once we get the cage then we will try housing them together again.

You can save $14.00 by ordering directly through martins cages
We looked at that, but the ferret store offers free shipping so it comes out a little bit cheaper. But thanks for looking out for me