Hello and thank you for your question.
You did the right thing by separating them. If one of them is bullying the other to the point of biting keeping separate cages may be the best thing for them.
Just because they were litter mates unfortunately does not mean that they will get along as they grow. The smaller one is obviously not fighting back and will most likely continue to be bullied.
clean the wound daily with antibacterial soap on a q-tip. You can also apply a small amount of antibiotic cream
Candy
Veterinary Technician
Practicing Veterinary Technician for 23 years. Veterinary Practice Owner, Technician Trainer