The social fabric and politics of giant communities will be all important to PC survival.
My giant communities are militant and divided. The strong lord over the weaker and there is anomosity between giant clans and types. Fire Giants tend to think Stone and Hill Giants are savage beast of burden who deserve to be second class citizens, and will not be biased if the party kills 20 of them (though a rare smart Fire Giant leader may see the importance of the lessers as fodder and military strength, which the PC's can counter by showing those lesser giants have already served their purpose, shielding their betters from the brunt of the PC offensive). However Fire Giants despise Ice Giants yet respect Cloud, Water and Storm Giants for their power, but will openly plot against Mountain Giants who challenge their domain (in my game, Fire Giants are the most numerous of the Giant clans and tend to form and lead giant communities, and human contact via elemental and other schools of magic are fairly common).
So the mindset of the giants and their respect for strength and utter disdain for the small and weak creates a unique diplomatic requirement, to be aggressive and strong mixed with condenscension and disdain yet respectful and proper, in giant fashion. I have met many players who revel in this role and are very good at it, as players enjoy being respected themselves, and enjoy operating from a position of strength. It is my belief that ALL parties of PC's are really miscreants and Lawful Evil at heart, chaotic evil when they KNOW they can get away with it. They cannot be that here.
RM is crit-master, so the fact there will be fights against quality foes means there will be injuries. Drawing from the wonderful simplicity of ADnD, I would hand out 10-15 doses of "heals any wound" potion. They go in with confidence, but not unlimited healing power, and if things get to easy, I can imperil the potion. This does not change the fact that the sooner the players turn this into a talking encounter, the better.
There are ways a GM can indicate the villians willingness to talk, an idea that is usually ruled out by players as they waste anything that moves. Giant families with nursing women and children need to run in fear of the invading monsters as they cry out, "EKK ITS A HUMAN MOMMA AND THEY ARE SO UGLY!!!"
Have young unskilled giants fight to protect the families and die doing so, in a rage and unwilling to listen as they try to protect their families the only way they know how: crush the problem. Let a PC or even Firegiant fireball toss broken giant child bodies around, one can create sympathy, the other display the absolute rule of the Firegiants and that they are answerable to no one.
A dead giant guard/adult lays at the PC's feet, and the giants being who they are, look down from up high and only hurl a threat or two at the PC's, commenting on how that guard was the weakest of him and thus stuck with the unpleasent duty of having lowly position of talking with violent fiends, and if they wanna real fight, well keep on coming. Then the giant walks away, alerting the community but walking away in very real disdain.
The more you make those giants real with thinking minds, the quicker the players will see they can parlay. After the PC's slaughter a few giants, you can even have two new guards talking to each other, wondering if they should parlay with these monsters who have already killed several of them and seen strong, while his companion shushes such talk as being above their simple station and besides, thats what dem lazy upper level ninnies do is talk. Rock Clan Giants CRUSH their foes...to say it a third time for players who need that sorta hand holding.
If not, throw 100 giants at them so they see they cannot win this via battle. Remember, Lawful Evil at their best, players always understand violence.
lynn