Civil will in Halacha

My father wrote a will only in a civil court, in which he determines what is to be done with his property after his death. Does such a will have any monetary validity according to Halacha for the sons, or does it have no halachic significance at all? And in such a case, does the mitzvah of “mitzvah lekayem divrei hamet” (the mitzvah to fulfill the words of the deceased) or the law of honoring one’s father after his death apply?

Shalom u-vracha 

A will that was made in this manner has no validity at all. 

The opinion of the Achiezer (vol. 3, siman 34) is that there is a mitzvah here, but in practice we do not rule in accordance with his view.

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