2 hermit crabs change shellshell

I cannot believe I got this on film! I have had hermit crabs for almost a year and a half. I have 3 pps that I've seen through multiple molts but rarely have they changed shell. Today all 3 changed.

[@tjdabear]

As an update, the bigger crab "Hermie" changed shells at least twice more and even harassed the other about his shell. He keeps picking shells too small for him. We bought the very expensive larger shells just for him but those are too big. We are having a very hard time finding something in between sizes. I don't think they have changed shells as much in their whole lives as they did yesterday. Any suggestion on finding shells would be great. I'm going to try MIchaels in desperation today.