I'm sorry that I'm two months late to this thread, and I hope that you'll still be needing this information. I have zero experience moving overseas with guinea pigs, but as an army girlfriend, I've looked into how I would possibly transport my guinea pigs if my OH gets stationed in Germany or Italy. (Maybe I'll see you there in a year if we do!)
Alitalia, while not a cheap flight, does not say one way or the other if guinea pigs are allowed in the cabin, but pets and food up to 10kg are permitted. You'd have to call and talk to them. (broken link removed)
Delta does not specifically prohibit guinea pigs in the cabin; the website merely says they will be accepted as checked baggage. If they fit in the same cage, they can be a two-for-one. To quote Delta's website, "Pets are accepted on a first-come, first-serve basis. Call Delta in advance at 800-221-1212 to arrange to bring your pet on board. *Exception: Two pets of the same type and 8 weeks (15 weeks for international travel) to 6 months of age may be allowed in one kennel, for example two dogs or two cats. They must be small enough to fit in one kennel provided they are compatible and must be of the same species and size, and they must meet the requirements of acceptance. They will be charged as one pet." You will have to contact Delta and see what they can do. Be prepared to try again and talk to more people. Have the rules in hand and point out when the agent contradicts what the website/policy says.
I read the EU rules for pets going into the country. Guinea pigs are not treated like rabbits or ferrets for customs purposes, so they DO NOT need microchips. It wouldn't hurt to have a recent vet's certification saying the guinea pigs are healthy. Getting through Italian customs you may take up to five guinea pigs: (broken link removed)
I am going to road test the Petmate Cabin Kennel Solid Top Carrier next week. I'm putting each guinea pig in a separate one, mostly because Lunch (the younger one/daughter) will shriek every twenty minutes as she tries to bury under her mother in terror, and I just want a quiet car ride. Lunch settles down when she's alone. The carrier is specifically designed to fit under an airline seat, but I'll be using it for a road trip. I think two guinea pigs could suffer through the 20 hour flight in one. I'm going to invest in some CareFresh for the carriers this weekend to see how they hold up to the pee during the car trip.
As for the actual travel: I'd pack watery veggies like tomatoes or cucumbers, their favorite treats, hay, pellets, water bottles/syringes to force water if necessary. Maybe you want to store up on some of their healthy poo from a day or two before the trip, just in case they need poo mash fed to them.
The good news is that if you can find an airline that lets guinea pigs in the cabin, there should not be much of a problem bringing them into the EU.
Final thoughts, I would not sedate my guinea pigs. Bring the carrier out during play time and put treats in it. Let them go in and out of it a few times before you put them in there for the big trip. For the flight itself (in addition to what I said before), I would maybe bring a blanket to wrap around the carrier, as I read in another thread that under the seats can be a bit drafty.