Everyone in the group wants to look for traps (magic and/or physical traps) and/or try to figure out more about who the statue is supposed to look like - possibly someone wants to be and guard/scout duty at the same time figuring out how if someone can be heard behind the doors.
That sounds like they're trying to have everyone do everything at once, which, nah. Question the players carefully and see what they're actually doing.
"Brother Gotha, are you looking for traps or are you studying the statue's face and robes?" "Ummm, I'll stay close to the doorway and study the statue." Okay, Cleric's going to
Spout Lore.
"Tinyfeets, how about you?" "I'm carefully moving around the room looking for death traps!" Okay, Thief's using
Trap Expert.
"Zalbar, what about you?" "I'm going to look for traps too!" "Okay, are you tagging along with Tinyfeets looking for mechanical traps?" "Ummm... no, actually, I'm going to cast Detect Magic." Wizard's
Casting a Spell. If he had said he was tagging along, that'd be an
Aid roll instead.
"And Jorg?" "I'll follow Tinyfeets around the room at a safe distance, but listen at each door as I come to it." Fighter's doing
Discern Realities.
So, actually, once you held their feet to the fire and asked what they were actually doing, it turns out that they're all making different moves, not stacking up on
Discern Realities.
Now, going to your particular questions:
1) "Their chances of figuring out every secret in the room is generally too good for my taste" -- why are you hoarding secrets? What good is a secret that the GM knows and the players don't figure out? But, no matter; each player is making a different move, so they aren't likely to find everything.
2) You don't tell them what to roll until they've told you what they're doing, period. The Wizard decided to cast Detect Magic, so if it fails, he still doesn't know if there's a magical trap.
3) Use first come first served in general, but keep an eye on who's getting screen time and who's racking up XP, and turn to the wallflowers every once in a while and say "what do you do?"
4) The definition of the Aid move is that it uses Bond. The assistance is applied to the character making the main roll, it's not applied to the situation. Aiding a
Spout Lore: the Cleric rolling 6 says "I know this statue looks familiar somehow"; the assistant says "oh, was there maybe an illustration in a tome in the monastery you were talking about the other day?" The assistant doesn't have the information about the statue, he has the information about the Cleric. If someone has a high WIS and a low bond, they can always do their own
Discern Realities rather than assist.