God- I am so confused! So, hubby is member of Qatar and earns Q miles whenever he flies. He has about 60,000 in the bank and wants to use these to take a OneWorld alliance flight (probably with BA) from Lhr to Rio. He isn't currently a member of BA Executive Club but can join any time. There is Avios availability and he would need 30000 Avios to do this oneway. Once he has joined BA, can his Q miles be converted over and does it cost anything to convert over?
Nope, you can't turn Qatar Qmiles into any other system, that's not how they work
As both Qatar and British Airways are part of OneWorld, you can redeem your Qatar Qmiles for British Airways flights. These will be priced at Qatar rates, not BA ones
If you take a look at the Redeem Qmiles on airline partners page on the Qatar site you can see how many Qmiles you need based on the flight length. There will be additional taxes and fees to pay with money on top of that, which depend on the airline and route
For a simple BA flight, you should be fine to redeem online using the Qatar partner booking tool. As a general rule though, booking partner awards is more troublesome than booking for the airline's own flights, especially when there are connections involved, so you might need to ring up for anything complicated.