what is he biting over?
If he bites because someone took at toy from him, take the toy away from both kids.
If he bites because he's angry about not getting his own way try teaching him belly breathing or ASL.
Sometimes she bites because another kid has a toy she wants or because she isn't getting her way. What is belly breathing and ASL? Sometimes she also bites when she is "wrestling" with us. We have stopped letting her "wrestle" but can't get the grandparents to stop it.