You're right. Danny brought this ending but on an unconscious level, but imo didn't want to end like this. When the involvment of his siblings in the cover-up was made clear and vivid by the tapes, his own objectives became clear to him : gain the upper hand in the family by any means and corner everybody until they admit fully. See last time they're all reunited just after he escaped the murder attempt at the motel, he is pressed by the time and spills the beans about the role of the mother. Did he want to kill John's daughter ? Certainly not, but it was a twisted way to push on John's buttons, a way to push them exactly where he wanted them to be and say stuff like "Danny threatened Jeanie because...you know Danny take girls to the sea and drown them...that's what Danny do...because he's the fuck-up of the family". He wanted them to show their true feelings about him, he loathed their constant lying. That's why he was so gleeful when John the boyscout finally snapped on that beach. But he didn't want to die right there, he wanted more of this drama with everybody until finally the truth comes out : after the death of Sarah, his father and the rest of the family made Danny the scapegoat, they poured all their darkness on him. Their success in life was only made possible because they cornered Danny in a dark place and let him rot there. It was a tragic process like in ancient times, almost a ritual sacrifice, only the father had enough spine (and evil) in him to know what they were doing on a conscious level. The children and the mother were too clueless and weak to admit to themselves what they did to him.

Danny wanted to bring everyone to their breaking point, it's only at that point that true forgiveness and healing can start, like in a therapy. But see, even the best of the them -John- cannot stand and face the prospect of a long and painful process, he couldn't "downgrade" (sorry for my english) himself and beg for forgiveness, he started shouting to Danny "how long, how long" and erupted in violence, completing the ritual sacrifice initiated by his father. Maybe Danny knew on an unconscious level that his project was doomed, that they were too weak to ever admit what they did, but he had to go down this road and try, and his siblings killing him was the second best thing that could happen to him. Wether they break and beg for forgiveness or they break and kill him, they will know now that their hands are dirty. They can rationalize all they want, because all the shit he pulled but what they did to their brother is a horror.

I'm not sure about the final twist with his son, but sure something must remind them constantly all what they did. I will watch the coming seasons to see them slowly descend into hell.