False fir against sign forgery

My father has served in Army for 22 years, when he was away serving his duties his brother didn't take care of the parents well yet there were 2 houses, 1 house is under the name of my father's brother and other on my father's name....he even signed on 50rs bond paper, now after passing away of their father he is after the house of my father saying there was forgery, now the sub inspector is taking one side and has registered fir on my father with IPC 336(3), 340(2)BNS, his service is at stake. When the SI has asked my father to submit all original documents my father didn't suspecting of a bribe by my father's brother, but my father has all the proofs