If you have a BA Premium Amex then you can use two companion vouchers in the one transaction. However, you would probably need to do the spending way before Jan 2014 or you will risk earning the voucher but not having availability.

A lot of people wouldn't agree with me, but I think that when you have a relatively small number of Avios available then it could be worth ignoring the companion voucher and using the upgrade route.

If you take your first option, you are left having to stump up cash for two CW tickets.

If you book WT+ and UUA to CW then it will cost you the 100,000 Avios that you are talking about with option 1, but the cash amount required may be nearer £3k, and that is without taking any account of cheaper costs/avios for the baby (I'm not sure of what they cost).

This may not work for this specific journey, but I've beed doing some calculations on a JFK trip for next year, and I'm tempted to go down the UUA route rather than use the companion voucher there. You also get the benefit of earning a nice chunk of Avios on the WT+ paid fare.

Depending on how long you have, it may be better to go down the Amex Gold Card route to get your extra Avios, but obviously you need to get the £3k spending in the next few months to qualify.