Why does returning false?

Question

Im working on prolog program for my homework.I have to find grandmother,aunt,uncle and grandfather , so I did something and its find the person what I looking for, after that returning false.

female(ayla).
female(pinar).
female(cansu).
female(dilek).
female(yaprak).
female(fatma).
female(muge).
female(nermin).
female(ezgi).

male(osman).
male(ulus).
male(cagri).
male(arif).
male(burak).
male(serkan).
male(talat).
male(cafer).
male(selim).
male(tolga).

parents(ayla,ulas).
parents(pinar,ayla).
parents(cansu,dilek).
parents(cagri,yaprak).
parents(arif,dilek).
parents(pinar,arif).
parents(pinar,fatma).
parents(fatma,burak).
parents(serkan,cansu).
parents(serkan,muge).
parents(talat,cagri).
parents(talat,osman).
parents(nermin,cagri).
parents(nermin,osman).
parents(osman,cafer).
parents(talat,ezgi).
parents(ezgi,selim).
parents(nermin,ezgi).
parents(cagri,tolga).


brother(ezgi,osman).
brother(ezgi,cagri).
brother(osman,ezgi).
brother(osman,cagri).
brother(cagri,osman).
brother(cagri,ezgi).

brother(ayla,fatma).
brother(ayla,arif).
brother(fatma,ayla).
brother(fatma,arif).
brother(arif,fatma).
brother(arif,ayla).

brother(cansu,muge).
brother(muge,cansu).

grandmother(X,Z):-
    female(X),
        parents(X, Y), parents(Y, Z).


grandfather(X,Z):-
    male(X),
        parents(X,Y), parents(Y,Z).


uncle(X,Z):-
    male(X),    
        parents(Y,Z),
        male(Y),
        brother(X,Y).

aunt(X,Z):-
    female(X),
        parents(Y,Z),
        female(Y),
        brother(X,Y).

my data(as a screenshoot)

functions as a screenshoot

and result