Well that happened quick

I've had this BTA now for about 7 months or so, it was just starting to get to a nice size, my tomato clown was finally acting like she might really host in it (mostly she just plays around in it for a while then goes off to her usual hiding spot). All was normal and fine on Tuesday evening, then when I got home from work yesterday and came down to feed, there were two BTAs instead of one. The new one is smaller, the original (?) is about twice as large, or approximately 2/3 of the size it was before the split. They are both still attached to the same rock only a few inches apart and both seem happy and healthy.
Now what to do next. Do I leave them both to co-habitate? Will they get along and play nice if I just leave them? Or, should I encourage the little one to move to a smaller rock and sell it? I'll have to wait and see how my clown takes to this new development. I was hoping the BTA would grow a bit larger for her since she is a rather large mature tomato. She barely could fit into the BTA before this

Is there a way to keep them from splitting and just get larger, and just how large will they get normally?
I guess this is not the worst dilema to have to face in this hobby
