This is one of those (rare) times I'll suggest heading over to Greg's Garage on facebook with this question.
He's travelled a LOT with guitars as have a few members over there.
I'll add to what @guidothepimmp mentioned - if you don't already have, get the best flight cases you can afford if the guitars will leave your sight. I travelled domestic (Kulula) with a acoustic in a heavyduty SKB flightcase - tried to take it onboard, but they stowed it in their carry on section. When I got back I noticed they'd managed to damage the case - one corner needed to be expoy'ed back on. Guitar was 100% okay, though - rather the case getting beat on than the guit.
When I was did some short contracts in jhb - I'd take a large samsonnite hard case, take the neck of my guitar and pack in the case between clothes. That worked realllllyyy well and meant I didn't have to lug around a bulky flight case on the Gautrain.
And do contact your airline - the rules are constantly changing - and get whatever confirmation in writing, something you can present at check-in/boarding - too many times has the story changed from what was discussed onb the phone and what you'll find applied at the airport.