She will make someone kill my brother and father - Please help me

Hi, I lost my mother 5 years back, after a year of her demise I got married, My father, brother and younger sister stays together, after 3 years of my marriage, my brother also got married, it was an arrange marriage, the girl was introduced to our family by one of our uncle (my father's eldest brother) without any further research and by trusting our uncle they got married. Since the initial days of their marriage, my sister in law's family tried to control our family matters, their negative influence on her was so strong and they often started arguing with each other and she got demanded. Her family is in different state, they make plans to meet without even keeping my brother in loop, they started giving shocking visits (her family plus their neighbors) and in front of her family she starts all the cries and do false allegation of my brother hitting her. Whenever she visit her parents she doesn't come back without making a scene and always stays there for 2-3 months. Now they have a 8 months old daughter as well. she has started breaking things, she has threatened my brother and my father - that she will make someone shoot them, she also said that she will make a false allegation of rape , dowry and domestic violence against my father, on 10th of November , there was function at her place , my brother took her to visit her family and to attend the function, she has not returned yet and her father is saying that they will not send her as we didn't like the food she prepare, we complain that either it’s too salty or spicy , last month my dad had liver problem so we asked her to prepare less spicy food for him- is this wrong ? she is spreading this in all our relatives and her relatives that we mistreat her, we have a maid at our place , the only thing she needs to take care is look after the family , as a homemaker this the least thing you could do. She took all the jewelry from the locker even my brother’s chain and few rings and saying it everyone that we haven't given her anything. Now she is roaming to all her sister’s places and didn't even bother to tell my brother about same, he calls her and ask if she is ready to come, he cries over the phone for his daughter, but nothing seems working for her, she always find reasons to fight. We also think that she have an affair as multiple times by brother has caught her talking on the phone , when question whom she is talking to - she broke the SIM Card , On her last visit at her parents place , my brother called her up around 12:30 Am , her phone was busy for up-to 25-30 minutes ,when he asked whom she was talking to , she replied it was Wrong number- these are few incidents which indicates the affair , but I may be wrong. The worst part is her family is supporting and covering her all the wrong doings, they are giving her bad teachings, and she is greedy, selfish and game planner lady (she is only 25) All she want is Gold , she always talk to her family that I haven’t gifted her or her daughter anything of Gold , I believe in gifting things which are useful- in front of me she accepted all the items very beautifully later she broke them , I was so hurt- still I never pretended and took the breaking as an accident. I don’t know what to do … I am scared for my father and my brother, we can’t trust her anymore , what if she come back and do all the sorry and later hurt them , she has already threated to kill them. Her one of the Sister’s husband is a very bad man and he can do all these things, we didn’t know about this earlier. One of his sister is a widow and have with 2 children, she doesn’t stay with her in laws, she stays with her parents and she is also a very bad influence.. We didn’t want her to come back; she is threat to my family. I am 3 months pregnant right now with my first baby; it’s getting way too difficult for me to handle or to understand this situation. Please help my family.