I think that Pete is Gigi's son and Chanel 5 is Boone's sister. Pete would have no blood relation to Grace, which is why she could be his love interest.
I think that Pete & Boone were the primary killers and they used Chanel 5 as bait to isolate or gain access to their victims. Since Pete got rejected from the Fraternity, he was working the newspaper to redirect evidance as needed.
I think that Pete killed Boone to protect Gigi. I think that Pete was sitting there having Thanksgiving dinner with Gigi. After he left, I think Chanel 5 killed Gigi.