IF you can show that he was mentally incompetent at the time he changed his will (or made a new one) and that somone exerted undue influence over time to get him to leave money to the Salvation Army, you could possibly have the will set aside in favor of either an earlier will, or  so that his assets will pass by intestate succession (in which case surving spouse, if any, children, if any, surviving parents, if any, and siblings,  like your mother, will take).Challenging a will is not an easy or simple process; you should consult with a trusts and estate attorney about this situation. If there's no enough money at stake to make it worthwhile to retain a lawyer, it's probably not worth taking any action.