oh yeah, got some more info.

If you are going to share the tank, you should take all the fish out,
rearrange the plants and rocks and stuff, so that any established
territory is erased, then introduce all the fish at the same time.
This is mainly for the females I think - if you are only going to get
two, then putting one in before you put the 2nd one in will give the
1st one a bully advantage over the 2nd one.

This is all basically info that I've read on the net and on this
newsgroup, so hopefully it's correct.