(b)in questions regarding succession, special property of females, betrothal, marriage, divorce, dower, adoption, guardianship, minority, bastardy, family relations, wills, legacies, gifts, partitions or any religious usage or institution, the rule of decision shall be--(1) any custom applicable to the parties concerned which is not contrary to justice, equity or good conscience, and has not been, by this or any other enactment, altered or abolished, and has not been declared to be void by any competent authority;
