I saw the translated trailer posted https://youtu.be/cG4tcLhmQ6E
It seems that initially Chrom is attacking humans, then he become the main character persona, if so that's open the possibility that other fire emblem chars can be "recruited" (that's a fire emblem mechanics too, so is completely possible, i guess) as evil mirages and make'em good mirages (or perfoma(?))
Edit: Got a hard time to put the link there, so i put the youtube's link, but you can find the source from one of the forum's topic: Third Trailer - Eng Sub