questions and spoliers

did susan's mother constance know that maurice had sex with susan when she was 14? was this the reason she wanted him dead? why did she marry him or did she find out about his relationship with susan after they married?

did maurice tamper with the video or did he just get lucky that the murder of constance wasn't filmed?

it was strange how maurice was willing to keep helen around after he finds out she was planning to kill him with constance. also strange that helen would stick around when she sees maurice screwing around with susan.

i won't even ask about susan's motivations.