If they avoid doing stupid things in stupid places with stupid people (as anywhere) there should be no problem.

Normandy is countryside. Paris (Paris proper not some of the projects obviously), especially tourist spots,  has cops and soldiers all over the place.

There are pick-pockets though. But hey I assume your brother has trained his family as a combat squad, right ?

I'm from Belgium and I travel a lot accross Europe.
I can say that Europe has never been so safe right now.
Your brother should go ahead and enjoy his holidays!
Aciram.