private function excludeFamilies($xref1, $xref2, $tree_id): array
    {
        return DB::table('link AS l1')
            ->join('link AS l2', static function (JoinClause $join): void {
                $join
                    ->on('l1.l_to', '=', 'l2.l_to')
                    ->on('l1.l_type', '=', 'l2.l_type')
                    ->on('l1.l_file', '=', 'l2.l_file');
            })
            ->where('l1.l_file', '=', $tree_id)
            ->where('l1.l_type', '=', 'FAMS')
            ->where('l1.l_from', '=', $xref1)
            ->where('l2.l_from', '=', $xref2)
            ->pluck('l1.l_to')
            ->all();
    }