So ... here are the rules for Coerce (from AoN):
So it says "a creature." The circumstantial attitudes referenced include "hostile, unfriendly, indifferent, friendly, helpful." It does not give guidance to impact a group.
"modified by any circumstances the GM determines"
That might seem vague, but there are a bunch of things you could give guidance on like relative positioning of people (should people further away be harder to intimidate?), situational aspects (they have more people than we do, they have authority, etc), or a plethora of other circumstances that would be important. They don't
need to because that's all under the concept of adjusted DCs.
[I won't even talk about how worthless the skill is because it takes a minute - but there's a feat for that, too.]
Coerce is a roleplay skill; it's not meant to necessarily be quick. Most coercion attempts don't involve a few spoken words, but a whole series of actions and statements to intimidate someone. It's not just "I spoke the magic words"... unless you got
Quick Coercion, then I suppose you are just that damn good.
For the GM to learn that there are alternative rules to coercing a group, they need to go to the Group Coercion feat and read that.
No, it says right there that it's for
a creature. Singular. You'd have to modify it to do multiple people, so you just add a situational modifier. Thus you don't need to read the Group Coercion feat because that simply
removes a potential modifier.
Also because it's a GM decision, you can simply say "Nah, in this situation I think the circumstances allow to do it unmodified", just like you could say "I'm going to let you do Coercion quickly instead of giving you a penalty for time" for some circumstances of the situation. What the feat allows you to do is to simply
not have penalties for certain things. Normally intimidating a group might be difficult, but maybe you're on a megaphone at a podium far above a stadium; in this case, the situation is built for you to not have that penalty, or at least not have
as bad a penalty (or we simply assume that it's offset by circumstance bonuses from the situation I described).
But also I don't get your solution, either: you want to give a bonus? Like, just straight up you're better at intimidating two people rather than one? I don't think that really works. Removing a penalty is the way to go, and the penalty is implicitly there, it just doesn't give firm modifiers because the GM should have freedom to set those as the situation demands. Unless you just want to start giving out Feats that are just numerical bonuses, which feels like a step backwards into 3.X design where you can start breaking numbers. And hey, if you want that, cool, but that's just not this game.
And how many feats are on AoN that a GM might need to read to learn the rules? 4,232.
Oh Jesus, let's get off it. There are only 243 skill feats, and ones like these don't even need to be known because they take away modifiers, don't create new ones.