Did you install any external art/patches on top of the hack? The hack’s technical stability was never one of its strong suits, but man these are some weird issues that I haven’t seen reported before. 
Which emulator are you using?
The area attack sounds like the artillery from Chapter 21, but there aren’t any houses in the final battle. At least, there aren’t supposed to be. And Anni is definitely not supposed to be usable there. Being able to re-use the already used unit may be related to part of the artillery logic’s instructions - I had to really jury-rig it to get it working, and I could see this being a side effect of that.
In fact, can you PM me or share your .sav when you get a chance?
Anni
She cannot be saved. A broad theme of the narrative is questioning whether the journey was worth the cost paid to achieve resolution and what stubbornly addressing insecurity can lead to. Not to say everything is Aaron’s fault - definitely not, more factors at play.
Lesbians
(For anyone jumping into the thread here: my earlier comment about this was a joke in reference to the prequel hack - there are lesbian characters and they are at the center of the story’s conflict, but they are not portrayed as evil or amoral or whatever. In fact, you could - and would be correct to - argue that the intolerance of their relationship is what led to the story’s conflict.)
The initial plan was to make a sequel, with Lydise as the main/player character journeying to right the wrong she committed & to achieve a better resolution for Ivos as a whole. She’s not meant to be a villain in any real sense; maybe I need to rework the prequel a bit to make that clearer. While Aaron would be present here-and-there in the sequel, he won’t be playable - at least not as part of the permanent party. But many of the original characters would be part of the party.
The monsters in Ch. 18, the prequel hack/FE4 tie-ins, and the intermittent comments about shady stuff going on in the imperial keep were the setup for a direct sequel. A broad outline was written, as well as a smattering of key scenes.
I planned to begin working on it between 6 to 12 months after this one’s release, but life/things change, as cliché as it sounds. I’d still like to do it, but there’s no definitive intention at the moment.