Harrasment & Threatening by wife

This is the matter of my sister's family in which My sister (Rekha),her husband,sister's mother in law, sister's brother in law(Sister's Husband brother) and sister's sister in law(anju )(Brother's wife ) liveing. Sister's brother in law wife(anju) is very rude & Quarrelsome . Because of her there is always discord in sister's family.My sister's husband is in government job so she is jealous about that very much and keep threatening my sister that I will deceive you in any charge.One day, there is bitter conflict between sister and anju and Anju threating that I will suicide and will deceive the whole family.In between that I asked my sister to record her video or audio recording of threating so sister did the same and have recorded some audio in which Anju Threatening of suicide and used abusive words to my sister and sisters husband.One day Anju's family members came and went off their daughter Anju and threaten that we will file a case against my sisters and my sisters husband.There is no case filed yet. Now what can i suggest my sister because She is in tension and depressed ? Is there any way to secure before Anju will file case against sisters family and if she will file a case then what can my sister do? Please Help Me. Thank you