Threy,
You mentioned that your parents had to book 13 days before departure to use Fly Smart?
How much advance time do you need to book normal FF tickets? In Australia, 13 days would be considered quite late - it is not uncommon for people to book tickets up to a year in advance (certainly a good few months would be normal).
Is availability of FF tickets that easy for LH M&M?
Cheers,
Justin