I do not have children and never will. I am considering getting married, but I would like to leave my estate to my nephews and nothing to my future wife. Is this possible?

No. In the absence of descendants, a surviving spouse who is not divorced is entitled to a reserved share amounting to one-quarter of the estate of their deceased spouse (French Civil Code, Art. 914-1). In the absence of children, it is not possible to deprive the surviving spouse of this right.