OK, tricky one!
Firstly, check with the dive operator what gear they provide. For example I provide all gear within my dive packages, divers come back year after year because I save them money, and baggage space.
If this is not an option consider replacing your gear with low volume / light weight. Most manufacturers now produce light weight / low volume gear for the traveling diver.
I recently bought an awesome light weight dive travel bag made by TUSA that complies with size restrictions.
Ask your self...
Do really need booties and fins? Full foot fins, if you are tropical / boat diving are much lighter, and take up a lot less space.
Do you really need to take first and second stage of your reg? Ask if your in resort dive shop will be happy to take your second stage and gauge / computer and put it on their first stage. If you are tropical / shallow diving it really won't make that much difference to the regs function.
Can you pre-ship your gear? We have had divers that send their gear by freight a couple of weeks before they arrive, we clear it and then send it back at the end of the vacation. Hard core photogs usually want to dive with their own gear, and bring all their photography equipment with them on the plane.
In practical terms you will need at least 1 bag each, plus your carry on. I would also suggest that as the airlines look to cut costs (reduce our allowances / number of bags etc) they also try to reduce the costs involved in bag management. It is more likely now that one of your bags won't arrive at your destination at the same time as you... so split 50 / 50 - put some of your stuff in your wifes bag, and some of her stuff in yours. That way you won't be caught out should one of your cases be delayed.
Lastly, invest in a camera vest, you can pack important stuff in the pockets, and it'll go through the security machines just like a normal jacket... or if you really desperate wear your BCD on the plane, again it'll go through security screening just like a normal jacket...
