It's not going to hurt them if they eat a small amount of it, but if they are eating a lot of it, then take it back out of the cage. Most small animals really aren't eating it. It may look like it, but they ususally just shredd it up really well. If ...
It may be best to keep them apart, as Chinchillas can get stressed easily, causing them pain and suffering. It's also worth remembering that it's a cat's instinct to hunt small furry animals, so make sure they are never loose in the same room togethe...
First of all congratulations on having that old of a gerbil! most gerbils don't live past the age of 3 or 4. But as for getting your little guy a companion i personally wouldn't do it. At that age he is a little bit too old to really accept another g...