What is the significance of the necklace, in that case?
We learn from the book that Sansa notices one of the beads is missing after Olenna adjusts it.
What about that several-seconds-long camera shot to look at the cut-into pie
I think it’s metaphorical - Joffrey’s savage slash has killed several of the peace doves that were supposed to be released.
Who wants both Joffrey and Tyrion dead, but Sansa safe?
Forget Tyrion, he’s accidental to this. One family wanted Margaery to be queen, but not with the loathsome Joffrey as king. That same family may feel some obligation to the girl they elbowed aside in the process. Sansa is also of interest to other parties because of her inheritance.