I assume they have done some homework. CityJet fly the Antwerp route from LCY 4x daily I believe, and Germanwings fly 3x a day average £100 return CGN-STN. (Personally I prefer Dusseldorf as a city to visit, but maybe CGN is a better business route). Groningen and Osnabruck were always on the cards.
Rennes and Caen; well, brave choices, but all six will need LOTS of continous publicity both sides. I wish them good luck.