Dragon Age Inquisition, option to recruit the mercenary isn't showing...

Did you get the Underworld Knowledge perk before starting the quest? That's how you recruit the mercenary.  Also, there's not enough statues to open all the doors, you have to save them for the stuff you really want.  There's only 10 statues altogether, if you already used them up on other doors, then there's no way to get into that room in the royal wing.