HCA: Hermit Crab Association

I recently acquired two crabs, Rinkydink and Meretricious. I've had them for 2 weeks. Rinkydink was pre-owned by a friend for several weeks, Meretricious was bought when we adopted Rinky. Meretricious has decided that now is a great time to surface molt. After much research and observation, it's pretty clear that's what's going on.
My question is, as he's already probably having a stressful time, rather than try to move a molting crab into an isolation tank, would it be healthier to move Rinky instead, who seems to be chill and content? Or will this just cause me to have two stressed crabs instead on just one?

If you are able to maintain two tanks, you could move the non-molting crab over to a different tank. But many of us can't have a separate set-up for another crab, so we would have to isolate within the main tank (using a margarine container with holes in the lid or similar).

Thank you. Do i need to sink the container quite deep so the other crab doesn't dig under, or is that not really a big risk?

If you are using an empty margarine tub with holes in the lid, you can just set it on the surface. If you want to use something like an empty 2L pop bottle with the lid removed and the bottom cut off, you can press it down into the sand so the other crab can't get under it (but this method doesn't work if any other crabs are underground).