If both you and Mrs Efin get a free BMI Mastercard, and then you and Mrs Efin each (as individuals) upgrade to the £60 BMI Premium Mastercard then you will get 4 x 20,000 BMI miles as welcome bonuses - total 80,000.

You only need 75,000 for 2 business class tickets to SFO (Star Alliance, so probably LH via FRA or United or US via LHR) on 'cash and miles' - the cash bit will be £255 + tax per ticket.

If you insist on First, you'll need to spend £10,000 on the Premium Mastercard - that will get you the extra 20,000 miles you need to get to 100,000 - the cost of two First Class returns to SFO in the BMI scheme (plus £340 plus tax, each).

Not sure what happens to the little one, though.