Genesis multiple category custom loop 404s after first page

Provided category names are not changing, and the site is in one language only, you could create two category templates: category-news.php and category-press-releases.php, then everything will pretty much work without you having to fetch the category and including the category__in parameter in the query.

Also, you always want to put your add_action calls inside your ‘functions.php`, not inside the template itself.