Complex sentence: On the day of her death Emily attended a seance held by a pair of local sisters, the Miss Tripps, both of whom say that when Miss Arundell spoke, a luminous figure came from her mouth.
Split into simpler sentences: On the day of her death Emily had been at a seance held by both Miss Tripps. Both Miss Tripps, two sisters who believe in seances, say that when Emily spoke, a luminous figure came from her mouth.