Recieved Suicide threat from sister in-law

Hello, The case is my elder brother got married in nov'18 that's a love marriage. After 2 months we saw some changes in her. She got hyper in small things whenever she got engry she abuse she throws kitchen utensils she say I will go my perents house. My mother is house wife she is very calm person she and i do all house chord sometime my sister in law do cooking things my mother never say anything to her. Whenever she got engry and do things we thought this is normally.... Har ghar m saas bahu or nanad bhabhi m nok jhonk ho jata h. And i thought she is new to our house its take time to adjust. In this 2 year many times she got angry and do same things after sime time become very normal. So we also forget but yesterday she start same thing this time my father and I not able hold ourselves and we also got engry we say verbally jo bhi hume khena tha then today she started agin she abuse my father infact jb m use smjhane gyi usne muje mara likely mene uspe haat nhi uthya or ye sub mera bhai dekhta rha pr kuch nhi bola mere papa ne kha ki aaj jo sub kuch hua m uske papa ko btunga after some time she became normal she eat lunch but jb wo apne kamre m gyi mere bhai k saat usne suicide attempt krne ki koshish ki jo saaf pta chal rha the ki wo ek threat h taki hum uske perents ko kuch na btay uske perents kolkata m rhete h or hum delhi m or uske papa heart pationt h isliy. So I just want to know how I protact my family kyuki agar isne fir s kbhi yesa kiya to uske perents schogne ki hum abuse kr rhe h fasegi to meri family na. Main yeas kya documents bnwau thaki agar future m agar ye kuch harm kre apne aap ko to responsible meri family nhi hogi pls suggest me taki m uske perents s bhi sign karwa sku.