Trying to be clear in a commercial transaction is equivalent to flying to the moon in a hot air balloon. If there is ever a dispute, lawyers will spend endless time and copious amounts of your money to prove you are either wrong or right depending on the side they are paid by to argue for or against.

That said, I assume the marketer, oneworld, would have no liability for failure to provide the the contracted services since the services are actually sold by an airline directly to you. If you bought them from an airline and one of the other airlines fail to deliver as promised, the airline that you bought the tickets from would have some liability similar to a store having sold you a defective iPod. I suppose, in this case, oneworld is sort of like a newspaper who publishes good deals but is not responsible if you buy an iPod that is defective based on a ad in the paper.

OTOH, see the first paragraph. Anybody can sue anybody for anything and frequently do, at least in the USA.

Cheers