HCA: Hermit Crab Association

In the center of my crab tank right now is a bag piece of driftwood. A few days ago my crab Crusty Sean dug out a space under the driftwood to get some privacy. Then, yesterday, my other crab Hermione moved in front of the hole and pushed some sand in front of it. Crusty is still down there and I want to make sure he’s safe, since I can’t see him without moving the driftwood and pissing them off.

If it had been just a couple of days, it is unlikely that he would have been molting - so I would think he could just push the sand back out of the way if he wanted to. Otherwise, he would have likely made a nice little cave, as long as the sub was a good consistency.

Ok. Update: he pushed up the driftwood and crawled out. Hermione came and sat on top of him on Monday. Then, on Tuesday, she had buried both of them. As of this morning, Hermione is mostly submerged and Crusty is chilling under the driftwood again, with all his legs out and a hole to the surface right over them (the legs). My main worry is they rarely moved until this week. Everything is fine I imagine?

I am not certain I completely understand. One is partly buried and one is totally buried?
What are you using for substrate, and how deep is it?
What are your temp and humidity readings?
How long have you had the crabs?