Since your father and mother is sponsoring you, you don't need separate affidavit for it. Include both of their names like I _____, father of ____ and I ______, mother of _______ is willing to sponsor OUR son/daughter _____ ....
About the army ranking thing, "Have any members of your family, past or present, held elected office, or held military rank of Colonel or above?"
Your father's cousin is just a relative and not considered as a family/immediate family member. So no need to get into that. Just tick the NO.
. Lol I didn't even realize that you posted your reply while I was preparing mine 
