JoAnn has posted some information related to chins on antibotics.
http://www.chinchillaclub.com/forum/index.php/topic,3476.0.html She says that greenish colored droppings are a sign that the food is not being digested properly and if this is not treated it could lead to a blockage. Loss of appetite may be a symptom of potentially serious problems. You need to find out which animal is having problems and know which is which.
Half-eaten pellets may be a sign of tooth problems. It could be that one animal is eating normally and the other is not. You should consider having this assessed by a veterinarian promptly.
Hope this helps