I have the amulet of Mara that I obtained from doing the quests in the Temple of Mara. I have not done all of her Radiant quests, working on those now.
Thinking about it, its probably because I havent spoken to Maramal yet... But he's never at the temple of Mara.
He's either at the inn or the temple and yes, you only need to talk to him and exhaust his conversations of marriage then you should be able to ask Aela.
You need to unlock the option for Marriage first, by going to Riften's temple, only then can you ask people to marry you. Also, complete Companions quest line, blah blah