Being they are prey animals to begin with and now in a foreign environment, it's natural for gps to look scared. Hopefully they have ample room as that will help. When I boarded Mooshy the first time with my exotic vet, it was at the hospital and the cage looked smaller than a pet store cage and it was metal. Side by side were cages, looked like a prison and I felt bad. I did take her igloo, sleep sack, and a couple of her toys along with her food and pre-prepared veggie mix and hay and bowls so they just had to provide the water. I wanted her to have her stuff that she's scented, which is funny because there is no competition! lol. Second time around I found a guinea pig rescue just over an hour away called Cavy House where they rescue and offer boarding. I found them to be awesome. Mooshy got her own 2 x 3 c & c cage! I took her igloo, sleep sack, tunnel for the home comforts and they provided KMS (or Oxbow if you prefer) pellets and timothy hay. Sooooooooooooo much better than the vet's office. Mooshy looked scared at the vet's office cage but she didn't look at me here and started exploring! She didn't seem excited to see me after a week but at the vet's office, she was sooooooooo happy to see me and get out. So for me she did "forgive" me for the vet's office but it was almost like I'm comfy, I don't want to leave at the rescue! lol
Either way, they'll be fine. After all, there's nowhere like home. They may start out skittish but that will go away with time. You can always give them their favorite treat that they don't often get as a welcome home present to help them settle in.