Our parrotlet, Midge, plucked for quite a while with no changes what so ever in the home. We did some research and believe it was due to breeding season and sexual frustration. We got her a mate, but she hated him for months
she finally stopped plucking now that season is over, so I think it's something she'll do annually.
My Severe is chewing up and picking his down feathers and I'm not sure why. He's only been home a week and a half and I think it's due to stress. His mother also picked him bald as a baby, so it could be emotional as well.
It sounds to me that Merlin is picking from the stress of the move and new additions to the flock. Kate explained it rather well. Do what you can for now, but wait on a permanent solution like a collar until you complete your move. Likely, the stress of moving again will set him right back
I've heard a LOT of success with King's Cages "Pluck No More" supplement, but it is a little pricey. Here's a link to their site if you're interested in reading a little more about it.
Do you have any photos of Merlin you could share? Then we could tell you how much damage he is doing and if it looks permanent