Hi I have a Question in prolog ,

I did it but its not showing answers When i ask about the brothers,sisters,uncles,aunts

This is what I wrote, what's wrong ?

/*uncle(X, Y) :– male(X), sibling(X, Z), parent(Z, Y).*/
/*uncle(X, Y) :– male(X), spouse(X, W), sibling(W, Z), parent(Z, Y).*/

uncle(X,Y) :-
  parent(Z,Y), brother(X,Z). 

aunt(X,Y) :-
  parent(Z,Y), sister(X,Z). 

sibling(X, Y) :-
      parent(Z, X),
      parent(Z, Y),
      X \= Y.

sister(X, Y) :-
      sibling(X, Y),
      female(X).

brother(X, Y) :-
      sibling(X, Y),
      male(X).

parent(Z,Y) :- father(Z,Y).
parent(Z,Y) :- mother(Z,Y).

grandparent(C,D) :- parent(C,E), parent(E,D).

aunt(X, Y) :– female(X), sibling(X, Z), parent(Z, Y).
aunt(X, Y) :– female(X), spouse(X, W), sibling(W, Z), parent(Z, Y).

male(john).
male(bob).
male(bill).
male(ron).
male(jeff).

female(mary).
female(sue).
female(nancy).

mother(mary, sue).
mother(mary, bill).
mother(sue, nancy).
mother(sue, jeff).
mother(jane, ron).

father(john, sue).
father(john, bill).
father(bob, nancy).
father(bob, jeff).
father(bill, ron).

sibling(bob,bill).
sibling(sue,bill).
sibling(nancy,jeff).
sibling(nancy,ron).
sibling(jell,ron).

And one more thing, how do I optimize the rule of the brother so that X is not brother to itself.