So I'm happy to report, that Dalton is doing much better! Him and Axel are getting along very well, and both of them have really calmed down and become quite tame. Dalton is walking much better, still not normal, but he is getting there! I think it was all down to an deficiency and previous living conditions. Thanks for all the help!
If his condition is improving with additional Vit C I would be VERY suspicious of the "high vitamin C" pellets you're giving him. Sounds like your guinea pigs will need to get 100% of their Vit C needs from the fruit and veges you feed him in future- or you could change pellet brand, or feed them a guinea pig vitamin C tablet daily, like the one from oxbow. Great to hear he's doing better now though, I'm sure he'll be able to live a very normal and happy piggy life with you!