there is not really such a thing legally as "next of kin" except for extremely limited circumstances. Anyone can name anyone as their next of kin. For making decisions, it is reasonable that your husband do it. For healthcare decisions, it dosent actually matter what a n-o-k thinks anyway, they will have their opinion asked, but then it could be ignored.
Are you thinking ahead to a will situation? Again, dosent matter who nok iis - the estate is distributed as per will, and in case of intestacy, it is distributed via intestacy rules (no nok needed)