Well first of all any chin that has a sudden diet change can end up with a bit of wet poop due to an upset stomach. It can take time for everything to sort out when giving a new food. The burnt toast is more to help stop diarrhea, and it used in a very tiny amount. A better option is to just pull the pellets and give hay only for a few days. A change in environment can also cause the poo to be off, so give them at least a week to settle in.
Second stop feeding the chins the junk food, a chins diet should be high quality pellet only food and hay. Good brands of pellets include, oxbow, tradition, mazuri, and some rabbit foods. The added junk in both the Carefresh and the Sunburst food can cause gut issues, along with a whole bunch of other health issues down the line. Chinchillas are not designed to eat fruits, vegetables, seeds, nuts, or animal products (eggs, hide, meat, bone, milk, etc) they are strict grass herbivores (certain herbs and plants in small amounts are ok, as treats).
Another possibility is that they are sick, so hopefully that are quarantined in another room from your current chin. A common cause of wet poop if you (or the previous owner) give them tap water can be a parasite called giardia (which needs meds to clear up). However the fact that the poops are small and round could also be a sign of a partial blockage and/or constipation. If the poops don't normalize within a day or two or they change for the worse (no poop, wetter poop, smelly poop, or blood or mucus in the poop) I would bring them into the vet to get checked out.
Acting fine doesn't always mean nothing is wrong, chins are great at hiding illness until they are at death's door.