Query to get last posts from authors of blog

get author ids instead of author nicename to get posts for muliiple authors using WP_Query();

$author_list = array();
foreach((array)$authors_list as $author) $author_list[] = $author->ID;

// make comma separated string from author ids array
$author_list = implode(',', $author_list)

and change wp query args

$author_posts_args = array(
    'author' => $author_list,
    'post_type' => 'post',
    'cat'  => $colecti_id,
    'posts_per_page' => '4',
);
$author_posts_query = new WP_Query($author_posts_args);