Fetch data from database from multiple tables matching condition
SELECT
    *
FROM
    listing_master_residential res  
    INNER JOIN listing_master_condo con ON res.Ml_num = con.Ml_num
    INNER JOIN listing_master_commercial com ON com.Ml_num = res.Ml_num
WHERE
    res.Ml_num = '$mls'


Also, instead of selecting ALL (*), select only the columns you will be using, this will help your query perform better.