my $input = {
    'Sally Smith'   => { parents => ['Bob Smith',    'Rhonda Smith']},
    'Betty Freeman' => { parents => ['Earl Freeman', 'Harmony Ellis']},
    'Betty Boop'    => { parents => ['Rhonda Smith', 'Louis McFern']},
    'Jim Morris'    => { parents => ['Betty Boop',   'John Wayne']},
};

##</code><code>##

my $people = {};
for my $m (keys %$input) {
    add_person($people,$m, parents => $input->{$m}{parents});
    for my $p (@{ $input->{$m}{parents} }) {
        add_person($people,$p,children => $m);
    }
}

sub add_person {
    my ($people,$name,%params) = @_;
    
    if(! defined $people->{$name}) {
        $people->{$name} = { children => [], parents  => [] };
    }
    for my $par (keys %params) {
        push @{ $people->{$name}{$par} }, 
            ref($params{$par}) eq "ARRAY" ? @{$params{$par}} : $params{$par};
    }
}

##</code><code>##

{
  "Betty Boop"    => { children => ["Jim Morris"], parents  => ["Rhonda Smith", "Louis McFern"], },
  "Betty Freeman" => { children => [], parents => ["Earl Freeman", "Harmony Ellis"] },
  "Bob Smith"     => { children => ["Sally Smith"], parents => [] },
  "Earl Freeman"  => { children => ["Betty Freeman"], parents => [] },
  "Harmony Ellis" => { children => ["Betty Freeman"], parents => [] },
  "Jim Morris"    => { children => [], parents => ["Betty Boop", "John Wayne"] },
  "John Wayne"    => { children => ["Jim Morris"], parents => [] },
  "Louis McFern"  => { children => ["Betty Boop"], parents => [] },
  "Rhonda Smith"  => { children => ["Sally Smith", "Betty Boop"], parents => [] },
  "Sally Smith"   => { children => [], parents => ["Bob Smith", "Rhonda Smith"] },
}

##</code><code>##

for my $top_level (sort keys %$people) {
    next if @{ $people->{$top_level}{parents} };
    print_level($people,$top_level,0);
}

sub print_level {
    my ($people,$name,$level) = @_;
    print "  "x$level,$name,"\n";
    for my $child (@{ $people->{$name}{children} }) {
        print_level($people,$child,$level+1);
    }
}

##</code><code>##

Bob Smith
  Sally Smith
Earl Freeman
  Betty Freeman
Harmony Ellis
  Betty Freeman
John Wayne
  Jim Morris
Louis McFern
  Betty Boop
    Jim Morris
Rhonda Smith
  Sally Smith
  Betty Boop
    Jim Morris