Query posts by a type and another type only if post is in specific category

Untested, but I think you’d need to do two separate queries and merge them together:

$args = array(
 'post_type' => 'featured-posts'
);
$featured_posts = get_posts($args);

$args = array(
 'post_type' => 'review-posts',
 'category_name' => 'featured-category'
);
$review_posts = get_posts($args);

$result = array_merge($featured_posts->posts, $review_posts->posts);

$final_query = WP_Query($result);