The dogs are almost 6 months old. By 4 months of our house, sometimes they are murderers, bite people, how can it be changed?

First of all, the most important thing is to warn the dog bite is wrong.
With the help of a friend: First of all, with the help of friends, the dog's fear of the dog is eliminated.
The food for friends to feed the food: When letting friends feed the food, let it see that the food is handed to the friend from the owner, so that it can understand that this person is trusting by the owner, not Dangerous figures
Ple together: After eating the food feeded by friends, the two praise it together, so that it can gradually get used to contact with people