[Weatherlight]

Would it help to set up several hideys, with at least a few near their starting point, so they feel safer exploring? Or a large cardboard box with the bottom cut out, so they have a large space they can feel protected in and still explore the ground and grass in there? Maybe they'd do better with gradual habituation so they have time to get used to the sights and sounds, like get them used to being held by an open window, then held in the doorway, then held outside, then put down? Although I guess that last one is too late =\

I hope they didn't pick up some pathogen or parasite when they're outside that's making them feel bad and fearful.

Not all small animal/kitten shampoos are well pH balanced for gpigs, and not all human shampoos are well pH balanced for humans, but I'd look for small animal/kitten shampoos that are advertised as such and then look over the ingredients lists and read reviews, if available.

You can trim their fur for hygeine and ease of grooming. How long is it now?