One thing I noticed while checking this out- at the beginning of C1, Marth is visible on the map in this spawn location for a few seconds while Caeda flies from the castle to Marth's fortress.
Considering your last comment, I'm assuming that this was intended to be Norne's spawn point? Once the map starts for real, he maintains this position:
And Norne takes this spawn point, while marth's goes to one of the cavs, who were in the bottom position in the base game iirc.
For clarity's sake, this was done using a previously unmodified ROM, on a Normal mode start, with the Hard Prologues mod on (just so I can test those later), And Norne was recruited without sacrificing anyone besides the sacrifice (I chose cain).
Here's the save file. NorneAlwaysTest.sav
Gonna go kill her off now, see how the game treats it for the next 3 chapters, then try the same thing in higher difficulties.