how much should a 4wk old kit eat?

I have 2 four week old chinchilla kits and unfortunately the two of them have torn up their poor moms nipples 😪. shes started barking and even bit them once. Ive been hand feeding them for 3 feedings a day trying to give mom rest. I feed them 21/2cc's of goats milk every 5 hours. Is that enough? Or too much? They love it and eat well from mom as well. Im juat not sure what amount they should be eating in one sitting. Also someone told me to add critical care to the goats milk? I havent cuz im not sure about that for kits so young.