Property dispute

My father has two sons and one daughtet which is me. My father married to my mother sister first but due to jaundice she died after giving birth to my elder bro. My mom took good care of him for 2years after his birth. My father married my mom as he felt my brother will be under good care of my mom . For 30 years there was no problem in our family .myself ,momand 2nd bro never treat my 1st bro as son of 3rd person.. but after his marriage . 3 months later he filed a case against my parents that he need his share of partition in the property because of father , stepmom and siblings harassment. And his wife filed a case parallel saying inlaws harrassment and dowry case against us.. actually the property worth is 1.5 crores and its my father's grandfather property. And deed of partition was done between my dad and siblings. The house s my father's dignity and he runs a bussiness for 45 years in that father gave 10 Lacks to go and settle in a separate house and to live them happily. They agreed that they will withdraw the cases and vacatte the house and leave .. but the wife of my 1st bro got the amount and withdraw oly her case . Now with that amount they are threatening us with gundas to give 40 lakhs . Or we should give 3 rooms of the house to live their .. my 1st bro advocate s threatened us without our permission he will sale 1/ 3rd share to another person... wat we should do now . Is it possible to sale 1/3 rd of share without my dad permission.please reply