The 3 families - Bondurant, Montvaillant, Belcastel - are connected by marriage in the south of France, with the families interconnected back to as far as 1000 AD. All 3 were deeply involved in the Religious Wars prior to the Edict of Nantes and in its aftermath, perhaps on both sides.
Does anyone know of a DNA Project involving these families? I ask, because I am concerned with a fourth family which may descend from the Belcastels. The proof, however, is difficult to find, and DNA evidence would indicate whether the effort to get documented proof would be worth it.