Find a family tree which contains an Uncle-Brother relation

uncle_brother.pl

male(donnie).
male(jimmy).
male(jethro).
male(cletus).

female(krystal).
female(ruthie).
female(blanche).
female(ruby).

person(A) :-
  male(A); female(A).

parent_of(Parent, Child, ParentOf) :-
  person(Parent), person(Child),
  Parent \== Child,
  member(Parent-Child, ParentOf).

has_parents(A, ParentOf) :-
  male(Dad), female(Mom),
  A \== Mom, A \== Dad,
  member(Mom-A, ParentOf),
  member(Dad-A, ParentOf).

same_mom(A, B, ParentOf) :-
  female(Mom),
  parent_of(Mom, A, ParentOf),
  parent_of(Mom, B, ParentOf).

same_dad(A, B, ParentOf) :-
  male(Dad),
  parent_of(Dad, A, ParentOf),
  parent_of(Dad, B, ParentOf).

brothers(A, B, ParentOf) :-
  male(A), male(B),
  A \== B,
  has_parents(A, ParentOf),
  has_parents(B, ParentOf),
  (same_dad(A, B, ParentOf);  % They share either a mom or dad
   same_mom(A, B, ParentOf)). % No solutions for same mom and dad

uncle_of(Uncle, Nephew, ParentOf) :-
  male(Uncle), person(Nephew),
  Uncle \== Nephew,
  brothers(Uncle, Brother, ParentOf),
  parent_of(Brother, Nephew, ParentOf).

uncle_brother_of(UncleBrother, Pivot, ParentOf) :-
  uncle_of(UncleBrother, Pivot, ParentOf),
  brothers(UncleBrother, Pivot, ParentOf).

uncle_brother(UB, Pivot, ParentOf) :-
  length(ParentOf, _),
  uncle_brother_of(UB, Pivot, ParentOf).

:- set_prolog_flag(verbose, silent).
:- initialization(main).
main :-
  UncleBrother = jethro,
  uncle_brother(UncleBrother, Pivot, FamilyTree),
  writef('Uncle brother of %w is %w\n', [Pivot, UncleBrother]),
  writef('Family tree: %w\n', [FamilyTree]),
  halt.
main :-
  writef('No solution\n'),
  halt.

Uncle brother of donnie is jethro
Family tree: [krystal-jethro,donnie-jethro,krystal-jimmy,donnie-jimmy,jimmy-donnie,krystal-donnie]

I haven't written prolog since college so true 'loggers might hate this.