Nesh-Shogta has not logged for a while so I'll try to answer, since I helped proofreading the 1st French version. It was a long time ago (almost 3 years) so take my answers with a grain of salt (at the end of the day, use your best judgement 🙂 ).
Almost. Aesir and Vanir are undead, Scorpions and Warlock are not. Heroes have to kill the Warlock as well.
Yes, I think so. Overlord just chooses the target/path and rolls for damage.
Yes. The mention of the warlock's area is just to help determining the rock's path, damage starts 1 area away.
Yes. Quicksand effects start on next Heroes' turn (as soon as the Hero tries to move).
Yes.
When all the picts & Thak are dead, Kerim & the Guards will attack the Heroes.
Though, you might rule ("hard mode") that the OL gets full control of Kerim & Guards as soon as all Heroes are free.
I believe it comes from an early draft of this campaign. Seems useless here, indeed.
Yes. Same as the 1st Complex Manipulation.
Yes, I think so.
The Lockpick gives an extra Gem for lock-picking, so if a Guard drops it, it can be used to help opening the chest without the Key (complex manipulation difficulty 2).
Yes, I think so.