Elder uncle took over business fraudulently What action can be taken

My father has one elder and one younger brother.my grand father has one oil business in kolkata.he has given three business to his three son.but when my grandfather got sick my elder uncle took over the oil business by taking signature from my grndfather without any prior knowledge.he kept all the money came frm that oil business which was supposed to be distributed among three brothers nd gave nthg.nw he is forcng my father to sign on documents as oil department are askng fr my father.how can i get justice??my uncle live at kolkata nd we live at bihar.