How to keep my mother safe from my father and elder brother?

We can't predict the acts of your father and brother to give a solution now.  If really there is any apprehension, move an application to bind over them under section 107 cr.p.c. before Tahsildar.

In case of any recurrence of past bitter acts by your father or brother, she has to  move an application under DV act for protection. You have to confide in any of your close friend or relative from your side to take care of the situation in your absence and move legally as suggested.

in previous any such incident occurred which prompted you to raise such query is not clear because raising dv case against husband and son in the absence of you will make her more worried because here you have forgotten that when you are out of country they only are the persons looking your mother and raising a dv case against them will complicate the issue and in other side the dv case will be protecting if any other person is cooperating her in place of you 

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