The function you are using, get_most_recent_post_of_user, won’t work as it only retrieves the latest post from the author. It cannot retieve a list of posts
Walks through each of a user’s blogs to find the post with the most recent post_date_gmt.
You will most probably be better of using either WP_Query or get_posts to achieve this.
You should first add all your author ID’s in an array or use a custom function to dynamically get them, and then use a foreach loop and loop through all the separate ID`s and using each ID in a custom query to retrieve the latest 5 posts from that author