I also wanted to know what should be my reaction when someone from my family does back biting? I've tried to tell them they shouldn't do it but they say what they're doing is not back biting. I've heard that not only doing but listening to back biting is also sin. If I move away while they're back biting, they feel offended that I'm accusing them of something which they're not doing

In the absence of them heeding to your advise, you have a duty to either not listen or simply get up and move away.