Crocster

Hello! So I'm new to the website so I hope I'm doing this correctly. I bought this pair of two budgies (one male and female) about 3 weeks ago and have been slowly gaining their trust. They've become tame enough to land and even eat off of my hand but recently they started biting my fingers when I take the treat away and they're still on my hand. Am I doing something wrong or is there something I can do to stop this behavior from continuing? At first it was just nibbles but they have just progressively been getting stronger in their bites and I don't want them to bite other people. Thank you in advance! (also forgot to mention they're both only a few months old)