...
my $from_parent_one;
my $to_child_one;
my $from_child_one;
my $to_parent_one;

my $from_parent_two;
my $to_child_two;
my $from_child_two;
my $to_parent_two;

my @pipe_handles = ( $from_parent_one,
                     $to_child_one,
                     $from_child_one,
                     $to_parent_one,
                     $from_parent_two,
                     $to_child_two,
                     $from_child_two,
                     $to_parent_two );
...
START: while ( 1 ) {
   ...
   # To be sure possibly remaining open pipe handles
   # are close before creating new ones
   #
   foreach my $handle ( @pipe_handles ) {

      close( $handle ) if defined openhandle( $handle );
         
   }
   ...