New to the show--predictions

Hey! I'm new to the show. I just watched the last 5 episodes on demand. So I'm catching up..if this has been said before so sorry.

But. I think all of the clues about a body and the "we need to talk" that the father was talking about has nothing to do with the silver bells killer. I think one of the kids isn't a Hawthorne. The mom or dad killed the kids real parent and then took him/her in. That's what the dad wanted to confess and that's the body cam saw being drug down the stairs. I think the kid they took in was Tess, the one married to the cop. (Her name is Tess right?) could be why they didn't find a match when the husband pulled hair from her brush. What are the odds he took the exact hair that was fake or that she got enough of it to fill a brush.

I think the silver bells killer is the older sister.