Please use the following patch of FEBuilderGBA.
//A unit that can perform Seize.
Main Character for Eirika's Tale
Main Character for Ephraim's Tale
Transport unit (Prologue and Eirika Ed)
Transport unit (Ephraim Ed)
//Auto cursor and status screen.
Auto cursor and status screen the unit at the top of the deploy.
If you want to use Seize or Transporter on more units than just two units you will need to rewrite ASM yourself.