In my opinion, I would seek professional advice.
They know how to remove a nest with the least possible danger for humans and should also know how to save the wasps.
Remember, some insects are protected by law, because they are threatened by extinction, and if they pose a danger to humans, solutions must be found as well that help both the customer and keep the laws.
I wouldn't flood a nest with water, because that would kill the young, helpless ones that still get fed. And the eggs.