The 68 degree thing isn't an absolute... for instance, if your chins' previous owner kept them at 40 degrees for the last few months, 68 is gonna take some getting used to. Same for any living organism. (that's an extreme example though)
There's ALWAYS going to be some adjustments when moving to an unfamiliar place... even for humans.
Poop looks healthy= good. And they're eating ok, right? Though with 2 chins in same cage it's slightly harder to monitor food intake.
If you're curious about temperature, ask to just borrow your grandma's portable AC for 1-2 days, and see if that makes any difference. You're probably right, and it's probably not temperature related, but it's not much effort to check and make sure, so why not? ... Also, temperature during playtime is more of a factor than temperature when just sitting around relaxing.
Anyhow, sounds good so far, overall, IMHO. I think temperature, food & water, poop, stress, are the main chin issues, and you seem to be keeping an eye out on everything, so I'll just cheer you on with morale support!