I know this question might look simple but I have never booked a package using multiple airlines. This year we flew Manchester to Miami via Heathrow. All flights were with BA, next year it is looking cheaper if the return leg from Miami is with AA. I can book it all through AA website but does anyone know if I can select seats at booking for the AA flight . Also when coming back and checking in at Miami the flight has a BA flight number but is on an AA flight so which check in desk do I go to. Any other advice from someone who has done this route would be welcome.