I have no direct experience but I have been told by other tandem couples that there are soft cases available that will fit a tandem with both wheels off the bike. If you don't divulge that a tandem is in the soft case, than you won't get charged extra by any airlines that charge extra for that sort of thing. If airline folks asks, just say 'its a bike'. Most would not know a single from a tandem anyway.

Once you get there, I would guess you would have issues noted by merlinextalight.

Santana is a premium brand and you will pay a premium price but all the coupled tandems are more. If you are only going to travel once a year overseas, is it worth the extra money to you? Also, the hassle of reassembling the tandem once you get there may offset the hassle of futzing with a regular tandem.