Complex sentence: Second and third-hand recollections of acquaintances suggest that Hay may have claimed to friends that he had written the letter, but Hay's children said they could not recall him ever mentioning that he had composed it.
Split into simpler sentences: Second and third-hand recollections of acquaintances suggest that Hay may have claimed to friends that he had written the letter. However, Hay's children said they could not recall him ever mentioning that he had composed it.