Sort subcategory archive by custom field

I’m using is_category to sort an archive by a custom field – works great. This category has subcats that I want to sort the same way, but the subcat archive sort reverts back to post date. How do I make the conditional revert to the parent cat conditional when a subcat archive is diplaying? Everything I’ve tried either gives me all posts in the parent cat, sorted correctly or gives me the subcats without the sort. Using:

if( is_category('32') ) {
$paged = (get_query_var('paged')) ? get_query_var('paged') : 1;
$args= array(
'meta_key' => 'lastname',
'orderby' => 'meta_value',
'order' => 'asc',
'cat' => 32,
'paged' => $paged
);
query_posts($args);
}

I can get it to work if I change the cat id to the subcat id, but that means I’ll have to have over 20 subcat templates, which I don’t want. Using an array of the subcat ids simply gives me the entire parent category. Thanks in advance.