I thought it was her little bro who got older and found proof that cosette was a lying bitch in the first timeline, so he found a way to turn back time. but ur theory sounds more interesting. i read a spoiler about who it was......
Read the spoilers. You're not too far off. Feom what I read, it wasnt twins tho, but I could be mistaken
I like
Your theory is great, just have a problem tho. If his the twin , how come his eyes are blue. Neither the first wife or the duke had blue eyes, so where did he get the blue eyes from ?. Im sure the one who reverseed the time was the mage in the mage tower. As you have seen around chapter 5 at the end ( http://www.mangago.zone/read-manga/actually_i_was_the_real_one/uu/d_chapter-5/pg-13/) you see a man, with blonde and blue eyes and in a hood doing magic. He was reversing the time. Those same feature's are then seen again with the lady teaching her about the gatherings ( which i believe is his mother ) and again around chapery 26 when the other lady ( which i believe is his sister) is helping her with the social trends ( http://www.mangago.zone/read-manga/actually_i_was_the_real_one/uu/d_chapter-26/pg-15/) . Its seen that her brother the mage has blonde hair and blue eyes. But it wouldn't make sense if his the twin of the blonde girl because he had blue eyes.
hmm yeah. i partly knew i was wrong on some facts but wanted to say my theory anyway lol
But who knows maybe there is a twist. Your theory does make sense.
THEORY WHICH MIGHT BE A SPOILER-
apparently the first wife had twins before she was killed but she made a deal with a demon to take revenge on the second wife, the parvis family, aka keira’s family. now the mom is dead, and demon takes over her body and killed one of her twins, the only girl, cosette, to take her body. so nobody lied about the prophecy there is only one girl who can contact the spirits, cosette is already dead. now the demon fakes the spirits and manages to kill keira, and make everyone else’s life hell including the dad.
but my theory is that the magician with time reversal magic is the twin brother who wasn’t killed. in the sources i read for my spoilers, the brother wasn’t mentioned again, neither did it it say he was dead; only the twin sisters was. so i believe the twin brother was left to die by the demon, seeing only a daughter can put the plan in motion and a boy not mentioned in a prophecy is useless. the other family we just met takes him in and makes the kid their own. i mean the side profile we saw doesn’t even look remotely the same as his now step sister. so maybe he reversed time to before the demon killed keira for her to come to him, and they make a plan on how to get the demon out of her. “but that’s a theory, a gaaame theeeory”