Once they split there is a somewhat open scar for a while. In the case of 2 larger ones, the maroons should not be able to beat them to death because they have 2 to spread the pain to.

Most likely the split was because of a double water change. Shipped from the supplier to the LFS (change #1) and then to your tank (change #2). If it was 2 in the store, it would have fallen apart long before they had it in the bag.

Once they find their cave or ledge to extend from in an optimal current flow, they will stay put for a long time. I have a group of ultra rose colored ones, all tank raised in my system and they move around very little even after splitting. Since yours was not settled in yet, it could go either way as far as moving goes. That can start as soon as the split scar heals up pretty good. The mouth may not be migrated to the center before they start to move if they decide to. As long as they are large enough, get fed after healing and have the light necessary, they should not get smashed to death by the maroons