I want to book a MAN-JRO (Kilimanjaro) trip for my son for a Uni field trip in May (travelling in Y). Main options are QR via DOH or KLM via AMS for just a single change en-route. I am leaning towards the QR option because he / we can accrue avios and if I book through my account on ba.com I can use an e-voucher held over from Covid which I might otherwise lose. I presume I can book for him using my account? He is in our Household account if that helps, but I think you can book tickets for anyone anyway?

BA.com is £20-30 cheaper than QR website for the same flights. You get 2x23kg bags on QR booking but only 1 x 23kg on ba booking and seat selection is 48 hours pre-fligth on QR but 24 hours on ba.com booking

On BA.com I seem to be able to choose either a mix of BA and QR coded flights for the same trip or all BA coded flights (with a couple of pounds difference on the fare for some reason). What advantage or disadvantage is there to booking all the segments as QR coded or BA coded? Any other thoughts ? I presume my BA gold card won't help him boook seats earlier unless we pay? TIA