I recently scheduled the job, like you had/have. In similar case, what I do is find out the dates of month that usually fall on day of week, for example 1st Monday usually fall between 1-7 and 3rd Monday falls in between 15-23. Hence, following crontab Should work for you

30 3 1-7,15-22 * * ['date +\%* = 1] &&

above cronhjob gets schedule for each day between 1-7 and 15-23 dates of month, however, gets executed only when the day of week is 1 (Monday).