Thank you for your replies :)
In one of the original concepts was, that the client would be the Emperor (similar to the second option of your thoughts), but I think, it would be better if the Mercenary would be a "third party" army of House Ordos (because Ordos has no enough "private" millitary strength to defeat all other houses).
In this case the Ordos "invites" the Mercenaries to the Arrakis, to help him to defeat the enemies of House Ordos.
- If the player is with House Ordos, then the Mercenary will join in later levels to the Emperor's coalition. In this case the Emperor - and later the other houses (joined to the Emperor) - gives a better offer to the mercenaries, to divide the Ordos forces. The player's task to show, that the Ordos can win the war without allies.
- If the player is with the Mercenaries, then the Ordos will join to the Emperor in later levels. In this case, the Mercenary will realize, that main goal is the control of spice (-> the Empire), not the defeat of the enemy houses. The player's task to build a "new house" from the Mercenary.
- If the player is with an another House, then the Ordos and Mercenary are allies. So in this case - in later levels - both Ordos and Mercenary are the member of the Emperor's coalition.
The Mercenary would be an "individual" organization, not a common term for mercenary soldiers.
That is due to a trigger error, doesn't have anything to do with the ini files. It's a mission scripting problem, so unless you know mission editing to fix it yourself, the only solution would be to contact the authors about it and hope for a fix on their side