The unnecessary time that would be spent making this game in Unreal would be better spent improving the game that has already been made using Renpy. The narrative base is good, but in my opinion it needs some adjustments, and the animations could be improved. Besides, making a game of this type in Unreal would take too long before we have new content to play.
In addition to focusing on new content and improvements to the animations, some changes related to the harem women and the protagonist's children could be made to enhance the game. I would do two things:
1- Each harem woman possesses a valuable talent in areas that would be useful when the protagonist regains his place on the throne. So if the player chose to make them allies and give them a position on the council, they could have more active roles in the narrative and perhaps achieve an important position in the future, once the protagonist completes his objective.
2- It would be interesting if each harem woman had a limited number of children, perhaps one or two, so that the game could treat them as characters in the narrative as they grow up (because if the protagonist's women had many children, it would be impractical to include them in the story). Then, they could create a new wing in the palace where the protagonist's children would live, so that he could spend time with them from time to time.(I'm playing as the protagonist with a benevolent worldview, so playing that way gives the impression that he cares about his children and sees fatherhood in a positive light.)