Hi!
I would say that your hamster is nibbling, not biting, as when my first hamster bit me, he drew blood (everything's fine with him now!). This could be because your hamster is stressed, they seem quite young so could be confused between your hand and a treat. I would recommend checking out ErinsAnimals or Victoria Rachael's videos on hamster biting, this might help.
Sorry if this doesn't help, i'm no expert
Cat