Thank you for your reply.
The Dwarven King is not informative on 'how to use the key', part at all:
And the Harmondale girl tells you how to use the key, only if you have selected PC with the said key in inventory (these kind of peculiar features are specific for this mod)
So if you speak with her and your hero has the Emerald Island Key in inventory : you get the right hint / information:
With the bad luck and stupid coincidence, I never spoke with her, while having the key in the inventory of my active PC.
So I had to learn how to use the key here on this forum
Just much later, after I play through this mod for 2nd time, I realized, I get totally different (and helpful) advice from her, when I have the right dude (dudess) selected...
And now I got the "Siege of Barrow Downs/Stone City", in less than a week I cleared the map and entered Stone City, but the King won't recognize the completion and no reward is given (I have the quest in my quest book, but he ignores me fully) And now I can't guess if it has to do with selecting the correct party member, as this quest is not item related.
Well, yet another quest will fall through.
Could not find the triggering event for Stone City siege. So I rather decided to load much older quick save.
The quest was not half bad. And I also learned, why I was not able to finish it the first time: As the city was locked, I town portaled to Nighon, and traveled from there into Stone City... which somehow broke the whole event setup and also removed "the gate is locked" from Barrow Downs to Stone City (as soon all spiders and ghosts are gone, it is at the locked gate, where you get the reward and also next follow-up quest)
And the follow up quest was also something I had to properly prepare for (also due short time limit)
I think the reason I was not able to find the starting even for the Stone City Siege, is that it is 'owned' by a "messenger", and not by the Dwarven King himself.
But the 'keep your friends alive' battle was quite a pinnacle. Compared to the previous quests / battles, I sensed huge jump up in difficulty. And there are still some battles + quests ahead of me. (I am also confused in where to find blaster trainers, I thought they should be in Celeste...and Black Magic GM - The castle in the Pit has the throne room locked... so I hope the trainer is to be found somewhere else)
I really believe that GM blaster + Soul Drinker will be the tools to make the fights somehow more manageable.