Since your first leg is BA, you will need to check-in via BA at least to begin with, and it's to BA that you will entrust any luggage. If online chack-in doesn't work then BA should produce all boarding passes for you, BA and Qatar are on the same system unlike BA and AA (for example). I would start with BA for OLCI and if necessary go to Qatar after that, but on the day it should be pretty seamliess.