Need to display tag group as first name, last name but sort on last name

A simple solution. Assuming either the slugs for these tags are authors last name first or can be changed to be so. You can change the orderby on the get_tags to be done by the slug instead of the default name.

$tags = get_tags( 'orderby=slug' );

If you can provide a more complete overview of where you are using these tags I can probably provide a better example.