Hint

father_of(X,Y) :- male(X),
                  parent_of(X,Y).
mother_of(X,Y) :- female(X),
                  parent_of(X,Y).

grandfather_of(X,Y) :- father_of(X,Z),
                       parent(Z,Y).
grandmother_of(X,Y) :- mother_of(X,Z),
                       parent(Z,Y).

sister_of(X,Y) :- female(X),
                  parent_of(Z,X),
                  parent_of(Z,Y).
brother_of(X,Y) :- male(X),
                   parent_of(Z,X),
                   parent_of(Z,Y).

aunt_of(X,Y) :- sister_of(X,Z),
                parent_of(Z,Y).
uncle_of(X,Y) :- brother_of(X,Z),
                 parent_of(Z,Y).
    

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