All I can suggest is to just give him time, if possible or necessary move him to a quiet room, provide plenty of hiding places. Our boy Alistair was very skittish when we first adopted him from a shelter. We put his cage in the bedroom and it was next to my fiance's chair, so during the day we would sit there and calmly talk to him and offer fresh vegetables. Now he is one of our tamest cavies, and will even eat pellets right out of my hand (none of the others, even the extremely social Cinnabun, will do this; if I open the cage and stick my hand in they move away and their "prey animal instinct" kicks in). He rarely feels the need to hide, and usually only hides behind the fleece hides if he's wanting to sleep. It took a couple of years, and a lot of patience and veggie bribes, or him to get this tame though.
He sounds a lot like Marshmallow. I found him in a box outside of work one day and he's also a big man (well over 1000g). It's been nearly 2 years, and he's still a spazmo. He does fine with floor time and lap time with the other pigs and snuggles with them. But, I've tried to introduce him to the cage with the three neutered boars and it was the same situation you have, and the constant loud noises and scurrying were making me crazy.
He lived with Cal, my heart pig, who was a dominant pig and was very sweet with him. Marshmallow really loved his older brother. When he passed away, he sank into such a funk.:-( My mom and I decided to adopt a pig from Critter Corral, and it turns out she's also a spazmo, and the two of them play "whack a mole" with their houses and run around like maniacs to their hearts content. They really complete each other. ;-)
How is Barley with people? Marshmallow is a people pig and likes to rest his big lips on our lips and cheeks and nibble/kiss us lol.
Also, you know the velociraptors in Jurassic Park? And the scary part where you realize they are smart and can problem-solve? Well, Barley is a velociraptor. He's been testing the cage divider and figured that that the zip-ties are instrumental at holding the divider in place. He's been working on them.
It's painful to watch. He wants to be with the other pigs but he has no sense of appropriate interaction. He does really well with people. I'm actually thinking of building a cage at work and taking him with me a few days a week. He really needs a lot of stimulation or he gets bored. And as we're discovering, a bored Barley is a naughty Barley.
We lost Frost on New Year's Day to cancer. Barley and Milo have been side-by-side neighbors ever since. We moved into a new house where they have their own room, and in the evenings, they have been getting supervised floor time and doing pretty well.
During the past few weeks, we noticed Milo and Barley both acting a little down after putting them back in their separate cages, so, on a day when TWP_2 and I were both home to check in on them, we took out the divider to see what would happen.
What we have now are two happy piggies. Barley and Milo have been together for about a week and are doing just fine. Yaaay!
But it's good to read that Barley and Milo are doing so great together! Barley's behavior at the beginning sounded like our late Chippy-Chippy. Some piggies are just clumsy to get along with others, but for Barley now the story is different and he has the friend he so badly wanted. :-)
Milo died yesterday morning. Barley was stressed and fearful much of the day. He understands what happened because he was at Milo's side when Milo died. Today, Barley is quiet and grieving in his house. We've taken him out for lots of extra cuddle time and we're on the lookout for a new buddy or two for him.
Here's Barley during laptime.