HCA: Hermit Crab Association

I have four crabbies and three are under. I've been building a larger crabitat for them and it's almost ready. (Moving from 40g to 55g) My question is, should I wait until at least one other is up and transfer them both at once, or is it okay to transfer one by himself? I don't want him to get lonely in case he's somehow chirping with his friends at night or something. But also, maybe he's not and hes already lonely? I just want to get him into the bigger crabitat so i can give him decent sized pools and have room for a shell shop, hides, and a flying saucer all at once. Thanks in advance!

If you are able to maintain proper conditions, transfer them over one by one as they come up. The one who is currently up won't get lonely if he's in the other tank by himself for a while.