Until someone with more expertise answers you, the first thing I would do is try to avoid departing LHR if at all possible. Oneworld flies to Doha and Madrid from Oslo on Iberia (per flightconnections.com) and to Doha on Qatar. I'd pay a little extra for the latter. I have Expert Flyer and would be happy to check whatever it was you wanted priced, but it won't give me YQ and other fees, just base fare. I use AA to book, at least I know I can reach them, lol, and the ticketing airline can't even tell you the final cost until they send it off to be priced. This sounds like a great trip.