hash → key: given name, value: somearray
somearray → reference to array of families
family → reference to array of given names

Not sure how you want it printed.

use warnings;
use strict;

my %data;

foreach my $string (
   'flinstones,fred,barney,willma,betty',
   'flinstones,dino',
   'doe,joe,jane',
) {
   my @family = split(/\s*,\s*/, $string);
   my $surname = shift @family;
    
   push @{$data{$surname}}, [ @family ];
}

# use Data::Dumper;
# print Dumper(\%data);

foreach my $surname (keys %data) {
   my $somearray = $data{$surname};
   foreach my $family (@$somearray) {
      foreach my $given (@$family) {
         print("$given $surname\n");
      }
      print("--", "\n");
   }
}
[download]

outputs

joe doe
jane doe
--
fred flinstones
barney flinstones
willma flinstones
betty flinstones
--
dino flinstones
--
[download]