I just finished the game, final escort mission for me was pretty easy. I just go long distance before zeppelin, destroying every balista , towers and nest. Only right before cutscene there was hard when zeppeling quickly lost healt, from 80% to 5% in less that 30!.

And Ygerna,pff, that was disappointing, way of ther ranger+ splitting arrows+close distance= her death. In less that minute.