The roots are very fragile at this stage, also, your stems are still very thin. It's risky to transplant right now. Not impossible, but risky.
I'd probably wait just a while longer, for them to toughen up. That will help them deal with the transplant shock a bit better.
When you do it, use a small garden shovel to divide the two down the middle of the space between them. Scoop out the one on the edge and have a new pot with soil all ready to go.
i would let them grow for another two weeks or so. Also Keep lights close so the don't stretch any more. When you do transplant you can put soil up stem a ways to make them a little shorter. The one that should be transplanted would be the one next to the side. The roots on that one will have less room to grow and root lock on side of pot. Happy Growing
I would do the transplant now before the roots have time to intermingle. One could carefully tip the pot as if transplanting a single plant and then carefully separate the roots and repot each plant. I did this just the other day with a mj plant growin in my cucumber starter box.