Is it a must to invite each attendant's parents to our wedding?
Not unless you're close to them. If your best friend from your youth is your maid of honor, and her mom and dad were like second parents when you were growing up, then by all means, invite them. But if you don't know a friend's parents very well, it's not mandatory to put them on your guest list. They don't expect to be invited.
See More: Guests & Guest List , Going to a Wedding? , Wedding Guests