Oh! Does one of the characters masquerade as the victim in each case? I remember SPOILER in Victory Ball one of the guests pretends to be the victim by switching costumes, Mrs Redfern pretends to be Arlena, and a similar thing happened in the Dead Harlequin, did it not?
All 3 Grew up with Sisters, Mark's Sister was Conway's Daughter, Jerry's Sister Moved To Lymstock with him and Iris's sister was the 1st Victim in Sparcling Cyanide
Conway's daughter was Mark's wife, not his sister.
Are they all tied to someone