You have to establish first that the memoirs contain defamation and lies - leave Bourrienne out if it since we have no idea how much of it can be credited to him.

Your statement that these were published to 'curry favour' requires supporting evidence: you need to know the date of publication for a start - Marmont wrote his memoirs in exile when 'currying favour' was no longer an issue - though defending his own reputation obviously was. Mme de Remusat's memoirs were published 50 years after her death.