Can we keep some of the interest money, and if not, who should it be given to?

Dear Mufti sahib! my father deposited some money in the bank in 1997/98, at that time he doesn’t know much about the interest, later on in 2008 he realized that extra money that bank will give to him is interest. so he decided to give the money to the deserved peoples. but my father died in august last year. i want to know. (1): that all the money of interest will be given to the deserved onces. or we are also able to keep some money of interest. because at the time of the deposit the value of the money was much greater than it is now. (2): if we are not able to keep the money, then to whom it may be given. (3): can we give it to our poor relatives, if they also know that the money we giving to them is the money of interest.