You're right at the part that the Dad was the other person who reversed time with the magician. But he didn't do it because he regret killing Keira, but it was all for himself. After Keira died Cosette revealed her true self and the spirits were angered, Cosette can't even control the spirits or whatever she doesn't have any power and so with that the kingdom fell into ruins and that made the father realized how stupid of a son of a bitch he is that's why he reversed the time. So all in all the Father is an asshole.
No, actually the grand duke doesn't remember anything from the first timeline, well maybe he does remember but only bits of memories from his dreams, only Keira has the full memory from the first timeline and that's why he won't be able to use Keira as he wants because Keira knows everything till the point of her execution. But from what I read in the recent raws when Cosette arrived, the duke's reaction was different from the first timeline, he asked Keira's opinion when Cosette claimed to be the duke's daughter. So far this is going on a different way from the first timeline, but still that doesn't clear the duke of what he did on the first timeline.
I think the 2nd person who reversed time with the magiacian from chapter 32 is the Duke. Because he had seen the past life the female lead death like the magiacian. And how could see that if he didn't reverse time it's not like the whole noble world knows there time getting restarted. and also no I'm not a fan of the Duke I fucking hate him more than anything. If I made any sense like dis oof or something idk.