First, if you haven't already, I highly suggest checking out this thread, which might have some answers (also, it's amusing). As for your specific questions, I assume this is for your PF2 conversion, so I'll answer in that context.
Lanathar wrote:
Are the party supposed to get full XP for all of them? Even if they don't participate?
For example I had one trigger at midnight with one PC and Aerys on watch. Aerys killed the two enemies before anyone could wake up with some great rolling
Should I give full XP?
Yes. As it says on page 507 of the PF2 Core Rulebook:
CRB p. 507 wrote:
Any XP awarded goes to all members of the group. For instance, if the party wins a battle worth 100 XP, they each get 100 XP, even if the party’s rogue was off in a vault stealing treasure during the battle. But if the rogue collected a splendid and famous gemstone, which you’ve decided was a moderate accomplishment worth 30 XP, each member of the party gets 30 XP, too.
As it says in this example, even though the rogue didn't fight in the battle, the rogue still gets the 100 XP from the battle. By the same token, even though the rogue was the only one to collect the gemstone, the whole party gets the 30 XP.
Lanathar wrote:
Also what happens with random encounters when the PCs go out an explore? Do both the PCs and the camp get rolls against random encounters in theory?
And what do people do if something attacks the camp whilst the PCs aren't there? Just resolve it yourself or take a guess at how you think it might go? E.g. if multiple cannibals attack at night they drag the NPC on watch away if they don't notice? Or does this remove too much agency?
You can see how it was handled in the linked thread above, but I think the answer is that this is ultimately up to you. The PCs should always have to deal with a random encounter (but not more than one a day, or else it gets kinda boring). If you want your PCs to be concerned about the safety of the NPC castaways, you should definitely have the camp have random encounters while they're off adventuring. It might cause them to reconsider whether they can leave the camp for long periods of time, or if they need to keep moving the camp so they are never too far away from it.
As for resolving an attack against the camp, I would resolve it yourself, unless the PCs have been dragging their heels. For instance, if they're dragging their heels about facing the cannibals, have the cannibals attack the camp and kidnap an NPC to move things along. The castaways can help you provide narrative pacing - use them for it.
Lanathar wrote:
Finally if the PCs have traps that deal damage to wandering monsters should them being "triggered" potentially give them a better chance at spotting the enemies? Due to cries of anguish/pain etc? For example I have someone roll a 7 on Perception against Jungle goats which I would take to mean looking in the wrong direction.
But a goat would cry out if they triggered a trap...
I don't believe there's any specific rule for that, but if you feel it wouldn't make sense otherwise, you could give a small +1 circumstance bonus to their Perception checks. I doubt it would break anything if you did.
