About False 304b ipc

Sir, my wife died due to natural death on 17 Maron the way to hospital. Her relatives blamed me nd my fmly ipc 304b and lodged an fir. I m a govt employee and earlier also during jun 2015 she drank acid and her parents lodge an fir but she herself gave statement to DM that she took acid by herself and her husbnd and inlaws are not guilty. After that she was under treatment till now and suddenly died on 17 Mar. Post martam report is yet to come, please suggest if PM comes as natural death than what police and her relatives can do to me and my family? I have 2 daughters of age 2.5 yrs and 1.5 yrs, married for last 5 yrs on 22 nov 2010. They gave name of my all 3 married sisters living with their husband in Army and my father, mother and brother who were at duty station of my father. At the time of incident only i and my little daughter and all neighbourers were there. Now they demand Rs 20 lacs for removind FIR, please tell what can they and police do if post martam shows normal or natural death?