spain
In Spain, relatives of a deceased person have standing to seek remedy against defamation, unless the will of the deceased specifies another person (even a juridical person) to have standing.
The relevant law is the Ley Orgánica 1/1982, de 5 de mayo, de protección civil del derecho al honor, a la intimidad personal y familiar y a la propia imagen (Organic Law 1/1982, of May 5th, on civil protection of the right to honor, personal and family privacy and one's own image).
The lies explained in the question match what is described in article 7, point 7:
Artículo séptimo
Tendrán la consideración de intromisiones ilegítimas en el ámbito de protección delimitado por el artículo segundo de esta Ley:
- La imputación de hechos o la manifestación de juicios de valor a través de acciones o expresiones que de cualquier modo lesionen la dignidad de otra persona, menoscabando su fama o atentando contra su propia estimación.
Article seven
The following will be considered illegitimate interferences in the scope of protection delimited by the second article of this Law:
- The imputation of facts or the manifestation of value judgments through actions or expressions that in any way harm the dignity of another person, undermining their fame or attacking their own self-esteem.
And article 4 states who has standing to protect the honor af dead person. Interestingly, to put a temporal limit, only relatives who were alive when the person died have standing:
Artículo cuarto
Uno. El ejercicio de las acciones de protección civil del honor, la intimidad o la imagen de una persona fallecida corresponde a quien ésta haya designado a tal efecto en su testamento. La designación puede recaer en una persona jurídica.
Dos. No existiendo designación o habiendo fallecido la persona designada, estarán legitimados para recabar la protección el cónyuge, los descendientes, ascendientes y hermanos de la persona afectada que viviesen al tiempo de su fallecimiento.
Tres. A falta de todos ellos, el ejercicio de las acciones de protección corresponderá al Ministerio Fiscal, que podrá actuar de oficio a instancia de persona interesada, siempre que no hubieren transcurrido más de ochenta años desde el fallecimiento del afectado. El mismo plazo se observará cuando el ejercicio de las acciones mencionadas corresponda a una persona jurídica designada en testamento.
Fourth article
One. The exercise of civil protection actions for the honour, privacy or image of a deceased person corresponds to whoever he or she has designated for this purpose in his or her will. The designation may fall to a legal entity.
Two. If there is no designation or the designated person has died, the spouse, descendants, ascendants and siblings of the affected person who were living at the time of his death will be entitled to seek protection.
Three. In the absence of all of them, the exercise of protection actions will correspond to the Public Prosecutor's Office, which may act ex officio at the request of an interested person, provided that no more than eighty years have passed since the death of the affected person. The same period will be observed when the exercise of the aforementioned actions corresponds to a legal entity designated in a will.
In summary, the principle "you cannot defame the dead" (stated in other answers), holds in the United States but it's not universal. In Spain, the families of B and C could sue the author to seek redress.