is there any way i can get data from two mysql tables at the same time

In much the same way as you joined cwd_attributes in your query, you can also join in cwd_membership and then check to see if the joined data meets your criteria.

Your query with an additional JOIN:

SELECT u.user_name as "Username"
     , u.display_name as "Full Name"
     , to_timestamp(CAST(a.attribute_value as bigint)/1000) as "Last Login" 
  FROM cwd_user u
  INNER JOIN cwd_membership m
    ON m.child_name=u.user_name
    AND m.parent_name='hr'
  LEFT JOIN cwd_user_attributes a 
    ON u.id = a.user_id
    AND attribute_name = 'login.lastLoginMillis' 
 WHERE
    a.attribute_value >= '1598824800000' OR a.attribute_value IS NULL
 ORDER 
    BY a.attribute_value;