you must focus and find if all the poop are small or not and from which one
little poop usually means eating less and its REALLY important to find it fast and if one of them eating less dont wait even for 1 minute and go to exotic vet
they are at risk of serious complications such as gut stasis, a gut blockage, dehydration and liver disease. It's extremely important to contact your vet straight away.
if vet was not available try to feed them the food they like most, if the sick one is not interested then yeah they have health issue and must be seen by vet and till then you must syringe feed him/her mushed up pallet or critical care food