Outstanding Questions

In answer to the first question I believe that the man was Robin's Mum's boyfriend/lover, or at least that's how I saw it.
Not too sure on the other questions but I think Johnno did tell Robin at some point, from what I remember...
And I think Al semi suspected that Matt killed Bob Platt but didn't really care or want to get involved as he was sort of on Matts side in a way. Plus I think when Robin realised there was a connection between Bob, Matt and Paradise she started investigating and thought there was something suspicious about his death considering the land had been sold to someone else instead of Matt, and then Bob's corpse turns up all of a sudden.

1) Who was the guy (with eyebrow tattoos) that was living with the mom? I thought that was Robin's brother but I saw a post somewhere else that said the brother was not in the series, but somewhere in Australia. They indicate he had a violent past with the mom.

Yes the guy was the mom's lover



2) Did Johnno ever tell Robin the secret he had regarding when she was raped in high school? He almost confesses to something (after he tells her he was in the truck when she was taken) but she stops him, saying she does not want to know. I had assumed he was somehow involved in taking her but I don't remember them ever clarifying it.

Yes he did. It wasn't really a secret. It was simply that he came out of the back seat of the car and felt he could have gone to help her but that he was a coward. I felt like they were trying to make it look as something more, then they changed their mind. It was blown out of proportion I think

3) Did anyone else think that the brothers and Matt accidentally killed Bob Platt in the beginning? I thought they were trying to scare him / hurt him a bit but they all seemed surprised when he died in the water.

It was an accident. I think Bob got a heart attack in the water or drowned, but I don't think they were trying to kill him. Of course they were heartless and just tried to cover it up when they realised he was dead.