Following my mother's death, the notary is requesting my parents' family record book to settle the estate. Unable to provide it, the notary is considering calling in a genealogist. Is this the usual procedure?

Yes, the notary in charge of settling an estate must establish the devolution of the estate (identification of heirs and indication of their legal share). In your case, the latter must ensure that your mother had no children other except you. Its role is all the more important as it could be held liable if the latter fails to do its utmost to consolidate the act of devolution of the estate. This is why the notary calls on the services of a genealogist, whose role is precisely to seek out any heirs who may not be known to it.