I know when I switched my Betta from flakes to pellets, he took a few days to realize they were food. He wont eat blood worms for this reason, but I haven't continually tried to feed them to him.
I would give your bettas a few days to realize that the new stuff is really food. I would give them one little pellet at a time, and if they don't eat it after awhile, take it out. Bettas can last awhile without food, so don't worry too much about you bettas refusing to eat for a few days. Also, the bit of food might be too big for your bettas to eat. When they start to eat if you see them having trouble eating a whole pellet, try breaking them in half with your fingernail.