thanks for the feedback.
Given that the party is level 10 (except for 1 character who is level 9), I let the paladin be immune and gave everyone else a Will save DC 27 (which the Mystic Theurge made).
Had the shaken state last for most of the time that the party moved south along the River of Lava while the icewall imprisoning Tyrus towered over them on their left.
Some scouting revealed the giants tossing boulders at the magmin, and the other one stacking iron ore.
The dwarven eldritch knight decided to try and lure the two boulder throwing giants in to an ambush. He headed south, said hello to them and as the encounter conditions indicated Hostile, I had them give each other a nudge and start lobbing rocks at the dwarf - who promptly turned and ran. The dwarf had stoneskin on, as well as expeditious retreat, so felt confident he could survive a few hits if they connected with a thrown boulder.
The giants followed, but still lobbed boulders from a distance - frustrating the party who were waiting for the giants to close. Greater invisibility had been cast on the rogue, and Haste on the party, and the clock was ticking down.
The dwarf finally moved so there wasn't direct line of sight and the giants then rolled in, spotting the other party members and getting ready for some clobbering. Indeed the giants did manage to land a few choice blows, but with the invisible rogue doing sneak attack damage, and the fighter getting a crit on one hit, and the paladin getting a crit with a smite, and the cleric catching both giants with an ice storm, and the sorcerer sucessfully "slow"ing one of them, the giants fell.
Feeling pretty good the party then decided to go for the other giant that they had seen - the one stacking iron ore.
The dwarf rushed ahead, not bothering to try and talk (which might have changed the entire complexion of the encounter).
Smack - the dwarf does a critical with the axe.
Smack - the giant hits back - 6d6+16 with an iron bar, twice - does 69 HP damage to the dwarf after the 20 points had been taken off the stoneskin, and uses his last attack to ring a big iron triangle that I had set up to be used if the giant needed to summon help to shift the ore.
As some of the party were still out in the passage looking out for others they were spotted by an Azer slave who had been sent to see what the giant needed - and the Azer then turned tail and ran back behind cover.
The dwarf and fighter dropped the giant and we finished for the evening.
The players though, know now that they are going to need all the healing that they have and more in order to be able to cope going toe-to-toe with the giants if the fighting continues.
With the boulder throwing giants gone, and the alarm raised it will stir things up a lot, and I'll see if I can crank up the heat on the party with magmin advancing from the lava and Azers getting involved while the giants are distracted.