i think Ed is sus too. Hes the one that gave the engagement ring, and also he wanted Scarlett to be a kind, soft spoken bride, which means he prefers a personality like Amelie. Im guessing both of them are in it together and they used some maids that dislike Scarlett haughtiness in on the murder
It's definitely the cousin, but damn! Ed you're so fast to move on dude, just wow!