1. Yes, the resolution of Lanie is incompatible with Gavin. It's not that jarring; you could simply imagine that Miranda stuck to her old ways and found a new child to exploit, I suppose? In any case, this is in no way essential to the mod, and should not deter anyone from installing it.
2. Yes, but it works perfectly fine to only recruit her for this adventure in ToB.
I really can't emphasise it enough - this mod should be in any and every install! It is as vital for ToB as Wheels of Prophecy. The side quests largely feel like filler, but the writing for the two main characters is superb and the whole idea behind the concept is refreshingly novel, yet still feels like it should always have been there. Seriously, the writing is so on point, it managed to completely reverse my views on a particular character, whom I had always thought to be of the more bland, puppy-kicking variety of evil, by way of a single brilliant sentence (you'll know it when you read it). It offers a completely new perspective and plenty of opportunities to roleplay Charname's grappling with their fate and future. I actually suggest playing it last in Chapter 9, straight after a certain encounter with a certain divine usurper (in fact, I feel Reunion should have been hardcoded to occur right after his appearance for story reasons, but I suppose it would be too easy to miss that way). This quest isn't about the fights anyway, and it fits very well as a last, personal denouement before the final confrontation.
The cherry on top for this mod would be some crossmod with Turnabout. A simple matter of adding some extra lines to the latter would suffice, but I guess it would be a mess to code with general compatibility in mind...
I hope Kulyok still skims these forums from time to time - if you do, thanks for all you have done for bringing Amn and Tethyr to life with some drama!
PS: Once again, the butler did it...