Davidsa - thanks but Squeezy doesn't appear to operate GVA-BOH in the summer. Last flight appears to be 25 April. It could be that they have yet to load their flights for sale, but given their baggage rules we are going to give them a miss, for this trip.
Fincastle - It's my better-half's Mother's birthday. And she is being driven from Newbury by her better-half! It does look likely that we will opt for travel by car from Heathrow (LX is currently cheaper than Squeezy to LGW for the dates we want)
So my objective is get the suitcases under 46kg, maybe I'll pack a Helium canister ... or two?
Phileas - I did look at shipping the bags - but I doubt that I could ship them to the Cruise company directly - and I don't want to send them to the in-laws. I couldn't find anyone on this side of the 'ditch' who showed any interest though.