here you need a "family certificate" (as we call it in Pakistan) which shows your parents head of the family (your grand father) and complete detail, DOB, name, gender of his family (wife/ kids) so it will show your parent ( father/mother) name on it and also the name of your uncle and with that just give a birth certificate or your “family certificate” issued in your father's name, you can also give your uncles high school certificate showing his parents name on it and your Father/Mother's high school certificate showing parents name with that give your birth certificate and mention the main points that how your trying to proof your relation separately
hope this helps...