Tiamet, first of all, wait until Ice Shard is almost upon you, then Dig underground. Dig below Jay, and wait until just before he's about to use Charge Beam, and then leap up to attack. Immediately dig belowground again, and emerge in FRONT of Chaucer before Shockwave hits, the electric attack should do no damage to you, then retaliate with a Draco Meteor at Jay.

dig//dig//dracometeor (jay)

Chaucer, after you get Shadow Sneaked by Jay, Crunch down hard on him and keep Crunching until he's about to use Charge Beam, then drop him to let Tiamet deal with him. When Tiamet's done, Facade Jay, and back off while Draco Meteor hits. Rock Slide Jay for more damage.
Crunch // Facade//RockSlide (jay)