Daughter in law is putting false accusations on me her Sister in law, how to proof myself?

This girl got married to my brother in November 2023 and it has been 4 months, 2 months ago she did the same thing lied to went to her parents and her parents encouraged her and told us to apologise even thou my mother was not at fault, she was mad at her husband for not giving allowance (my brother just got a job, and he is already paying loans) anyway her parents always take her side and never teach her good values. We never took any dowry or anything but they said they wanted to give 1lc for furniture which we denied but they were too eager so we accepted and bought the furniture, for their room. For 4 months she has been mentally torturing and abusing my brother, for many things mostly allowance even after her husband does everything he can to provide for her, but her food and everything is cooked by my mother and me and she never does any work not even her husbands. We don’t force her to do any work cause we know we want our Bhau to be treated good, but she took it for granted. 4 months my mother and I have been washing her clothes, cooking her food and doing all her chores and never does a single work for her husband, not even making breakfast for him. My mother and DIL had a small argument which was resolved but she called her mother and started lying that my mom is scolding her and stuff but I was there as witness and no one was yelling or scolding, so my mother straight called the daughter in laws mother and spoke to her saying it’s iftari (breaking fast) time almost and we need to prepare but she keeps calling you and talking and lying. This day on 16th March 2024, all the above happened , DIL was on video call with her parents and screen recording was on where I her SIL tried to put her phone away in a good way but she moved her hand a lot and now she says that I hit her, and proof is the video recording of the video call but it has no voice, how to proof that I was innocent, in that screen recording I think it shows that I’m raising my hand on her but now she says that I hit her and her hand is aching and when she was here we did her checkup and she was not pregnant but now she is at her home and says she is pregnant and asking for allowance for expenses, we asked for report for the pregnancy but they won’t answer. AnotheR thing her Dad is calling my uncle and threatening him saying that he will kill me and punch my face and lot of stuff. Please tell me what can I do about the video recording which is a lie and now they are threatening to do a case and what can I do about her dad threats?