I've got a couple of questions about the Aid Another action.
Specifically, as it applies to the Helpful trait, the Order of the Dragon cavalier order, and the Bodyguard feat.
1. What happens if you have both Helpful, and are a member of the Order of the Dragon?
Whenever you successfully perform an aid another action, you grant your ally a +4 bonus instead of the normal +2.
At 2nd level, whenever an order of the dragon cavalier uses the aid another action to assist one of his allies, the ally receives a +3 bonus to his armor class, attack roll, saving throw, or skill check. At 8th level, and every six levels thereafter, this bonus increases by an additional +1.
How would these two abilities interact with one another?
I'm sure this isn't intentional, but it looks to me like the Order of the Dragon ability doesn't replace the +2 bonus from the normal Aid Another action. Yes, this is a silly interpretation, but it's what the ability literally does say. An Order of the Dragon cavalier seems to grant +5 by himself when he aids someone. Then, add that in to the Helpful trait, which takes the normal +2 and replaces it with a +4. What then? Assuming Order of the Dragon replaces the +2 with a +3, can it stack at all with Helpful?
Personally, I am assuming Order of the Dragon is not intended to stack with the Aid Another it is modifying. Just pointing out that the wording doesn't actually indicate this.
2. Can you Aid Another on someone you're already Aiding?
Multiple characters can aid the same friend, and similar bonuses stack.
If you Aid Another as a standard action, then spend an Attack of Opportunity to aid the same person using the Bodyguard feat (or the Swift Aid feat), do these bonuses stack? I can't see any reason why they wouldn't.
3. Swift Aid - how does this one work?
As a swift action, you can attempt the aid another action, granting your ally either a +1 bonus on his next attack roll or a +1 bonus to his AC.
Seems to me that an Order of the Dragon could swift aid at +3 (or +4), but a Helpful person could only aid as a swift at +1 (since their +4 only replaces a +2 - and Swift Aid is only a +1).
As I see it;
1a: If you have helpful, I would assume that you start with a +4 base number instead of the standard +2.
1b: I am fairly certain that the meaning of the Order of the Dragon ability is a +3 instead of +2, or a basic +1 additional bonus at each iterative level of the ability. Reading it as an additional +3 is taking a great deal of interpretive license... not to mention that it fails the common sense test of, "Is this ability at 2nd level wildly overpowered compared to comparable abilities?".
1c: Given a and b, I would say that the Order of the Dragon ability being a progressive additive bonus would use the Helpful base number of 4 and add 1, so instead of being +3 at 2nd level, it would be +5, then progressing every 6 additional levels.
2: I do not believe a single character can provide multiple aid another benefits to the same attack. You cannot parry twice, nor double block with your shield, so no, a single character can apply one benefit of aid another to another character for one attack. The AoO usages could be applied to follow up attacks, but not stack with the original. The similar bonuses stack portion of that sentence is clearly linked to the first portion, that multiple allies can aid the same friend... there is no mention of a single character being able to duplicate the same action.
3: Swift Aid is a bit tougher to adjudicate because it's wording is so brief. It could be a simple case of being 1 point less than normal base, or half of normal... but then with either of those possibilities how would you determine how either ability modified that number, if at all? Would the Helpful grant a +2 and bring it to +3? Or simply double the amount to a +2? Or not apply at all do to the limited wording? Would the OotD grant it's standard +3? Or would it be a +2 on account of simply improving the AA by +1? That one leaves a lot open to GM evaluation and is highly dependent on how you rule on the first question.