Filter the WordPress author link to point to the author's BP profile rather than the WP-standard author post archive.

filter-author-link-to-bp-profile.php

<?php 
/**
 * Filter all instances of the_author_posts_link() so that the "author link"
 * no longer points to the WP author archive at /author/username
 * but instead points to the BuddyPress user profile at /members/username.
 *
 * @param string $link   Calculated link to the author's archive.
 * @param int $author_id ID of the author.
 * @return string Link to the user's BP profile.
 */
add_filter( 'author_link', 'dc_bp_filter_author_link', 10, 2 );
function dc_bp_filter_author_link( $link, $author_id ) {
  return bp_core_get_user_domain( $author_id );
}