marriage

When both of them are willing and decided to live separate why do you want to spoil their married life, wherein both of them threatened/ tried to commit suicide, if you thrust your wish upon them .Let them enjoy their life, they may return to family when good sense shall prevail upon them.

"sister in law wishes to get separate.. and

my brother does want to get separate.

so she started saying she will commit suicide..

my brother even tried to commit suicide

The issue is not litigation.  If you want peace in the family, convince your brother and let him take a decision to live separately with his wife.

Because the members offer certain guidance it may not reach your sister in law, and she can never be convinced as she is stubborn on her stand.

This does never mean of disowning parents, and still  parents can be taken care of in all ways if there is a will
 

Thi is a socail issue,since your sister in law is willing to put up seperately let her,it is better for the peaceful enviroment. It looks starnge though ; if you can put some socail presuure upon the family of sister in law by calling her parents and siblings through neighbours and other elderly relations to make her sccumb to her evil motives. Even file a report i n police station that she is threatning to commit suicide, make recordings and keep evidances.

The posting suggest confused thinking and ideas on the part of the author. It is the best course that a married couple are left to take their own decision.

They should be prevailed upon to go for professional and competent counselling. Family members, esp. parents and siblings, would neither be detached or objective.