Few questions on this topic..

I'm about to run game with all 3, as my players picked classes from all books.

I have 1 AoTE, 2 EotE and 2 F&D players.

All of those starting traits have a table in which you give players starting value based on numbers of players.

Should you use the whole number of players now (ie: 5 players, so they get Obligation of 10) , or just the number of players using classes from same rulebook (ie: I have 2 players from EotE, so i would give them starting Obligation of 20).

Further more, should you give now to all players all 3 traits, or just the one their class have? Or maybe 2 of those traits to each player? And if so, what will that do to the starting point in each of the traits?

I'd base that more on the campaign than the character choices, eg: I run an EotE campaign, but 2 out of 3 are AoR careers. I still used Obligation to start things off. Obligation is more for campaigns where the PCs are cash-strapped and owe somebody; Duty is more for campaigns where they belong to a larger organization and need to make there way in it. You can run both, but personally I'd just pick one.

Morality might be different, you'll need it for the F&D characters, in addition to whatever else you use for the others.

Yes, i figured it out that it is based on campaign, but how do you determine starting values of Duty/Obligation?

you have 2 AoR careers...did you give them starting Duty based on 2 players, or based on 3 players you have in total?

I would give them no duty but Obligation.

Yes, i figured it out that it is based on campaign, but how do you determine starting values of Duty/Obligation?

you have 2 AoR careers...did you give them starting Duty based on 2 players, or based on 3 players you have in total?

If you're going to use these mechanics, it's probably best to apply them to the group universally (except Morality).

In my case, I gave them no Duty at all, just let everyone pick their Obligation (for extra XP) and didn't assign any to the group. Before I explain why, maybe a return question:

What is the campaign centred around? What need do you have for any of the mechanics? How will using any or all of them be useful to you for your story?

If you don't need them, don't use them just because they're in the book, just pick what you need for your campaign. If you just need something so the characters can get some extra XP, then pick Obligation, it's simpler.

Personally, I have little use for Obligation past character creation, I let them start with what they want, and it helps set the initial stage (including identifying possible recurring themes). I don't use it to trigger events or impose Strain or limit XP. If I want to impose those things they'll be based on the story at hand, not a random die roll. I found including them takes away from the RPG aspects and makes it more of a "card game" or something.

I'd probably feel the same about Duty because it's tied to character progression in an organization. It might be useful at chargen to help define the character, but the story might have nothing to do with "rising in the ranks" or a character triggering their "Intelligence" duty, so I wouldn't use Duty.

The book recommends that you just base it on those who actually use the trait in question. If everyone has Duty then everyone counts towards it. But if only one person then you only account for one PC. But that's what the book recommends.

I'll second whafrog's suggestion, and that rather than trying to combine Duty and Obligation, you instead pick the one that makes the most sense for the theme of the campaign you're looking to run. Force users would still have Morality on top of having either a Duty or Obligation.

This way, it's simpler to track what the group total is, and increases the likelihood of reaching 100 in either Duty (good) or Obligation (bad) for the group, and you're also not dealing with instances of the PCs suffering a reduction to their strain threshold from somebody's Obligation triggering while also having a wound threshold boost from another PC's Duty getting triggered.