Nevertheless, in view of the world-wide notoriety which attended it, I have been asked, both by my friend Poirot and the family themselves, to write an account of the whole story. 
Poirot and the family all wrote the same account of the story.  
mnli hypothesis: Poirot and the family all wrote the same account of the story.   premise: Nevertheless, in view of the world-wide notoriety which attended it, I have been asked, both by my friend Poirot and the family themselves, to write an account of the whole story. 