I think Kratos is Tyr. He certainly looks like him. Atreus we know now is Loki who is the father of the world serpent according to Norse Myth and possibly why the world Serpent tells Atreus he looks familiar.
Since the cycle must break and Kratos is known to have changed his own fate, I think this trilogy might not be a trilogy or as straight forward.
1) it could be that Kratos has to go to other mythologies to find ways of beating Odin and Thor.
2) we play through the norse mythology and when Ranarok ends and the world is drowned in water, Kratos goes to Egypt to bring land back to the world.
I don't think father and son will be together through every story as children eventually grow up and leave their parents. The vision of Thor at the end of the game also might hint towards Kratos being hit so hard, sending him to another land / myth since fate is being rewritten.