What should I do???, Biting

[Edward's Mommy]

I have a question. For a while, Edward used to bite. And I got him to stop. But lately, he has started again and he only bites two people....my mom and my friend's 2 year old son. They are the ONLY two people Edward bites. My friend is pissed off at me because Edward still bites. I know that when he bites my mom, she bites him back. I have a feeling that with her biting him back. he's getting the idea that it's okay. Since right now, I live with my parents, there isn't a whole lot I can say. Every rule I lay down for Edward is ignored or undermined. I don't know what to do. People tell me that I should bite him back. Plus, it's hard for me to punish Edward for biting, when I never see him biting these two people. My mom says he bites her, and my friend's two year old has a bite mark on his arm from time to time, but I never witness it and no one else does either. What should I do??

[Edward's Mommy]

Sorry, this is the wrong area!