BA seems to be $17,686 in Business Class for four for SFO-LHR-LIS-LHR-SFO. If BA and AARP extend their discount offer beyond August 31, you might save $200/person off of that fare by joining AARP for $16. If you were to get the Chase/BA credit card ($95 annual fee) you would save 10% off of the total fare for all four passengers. Details here:


https://www.britishairways.com/en-us...visa-signature

You'd have to investigate whether any blackout dates apply.

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Edited to add: If you got the Chase/BA credit card, you would of course need to have a sufficiently generous credit limit to get the discount for all four passengers, as you'd have to charge upwards of $16,000 in one transaction.