I don't know what to do.

So I'm so stepmother to three wonderful children, 14, 13, and 7. Lately the 13 year old has been very defiant and even stayed up on his computer until 4:30 in the morning. We had this issue before and my husband told him next time he would lose the computer. Well it didn't happen. He's been caught a few times on it after we told him he couldn't be on it but no punishment has resulted. He told my husband that he's upset about this girl but I think he's just being a brat. My mother is in town busting and he has been completely rude towards her. Yet he has not apologized. I'm doing my best to stay out of it but it really upsets me because it keeps causing issues between me and my husband. I honestly don't know what else to do.