A 30 gal is only big enough for one. You'd want a 60g for 2. They will almost certainly get along as juvenilles. When they get older it's hard to tell. Better odds are when they are kept together from a small size. They seem to be healthiest at 1.015SG or higher. It just makes it easier to keep them at full marine since then you can use protein skimmers and
LR to decrease your need for huge waterchanges. Plus then you can have a few tankmates with them sometimes

And new evidence has suggested that they are marine breeders... but anyways, I won't get into that now
