I concur. You just need to keep handling them. Burms tend to calm down with handling and age/size. Are these captive bred snakes? It does make a difference.

Usually once a burm gets truly large, if you handle them, they rarely bite. I don't give them much credit for being smart, but once they lose their fear of you and they realize that you are not food, they usually do not bite.

I can't even tell you the last time that I was bit by a burm over 10 feet long.