I just do not ever see actual romance ever happening between the adopted daughters and Kaiser. As they said, Kaiser is just too proper for that. He'll never see them as women. If he does, it'll be such a turnaround and out of character that it'll be crazy. And even if then, there are three of them. Who tf would he choose? Even if he somehow did end up being willing to be in a relationship with one of them, who'd he choose? He'd never leave the other two extremely disheartened and disappointed like that. And he's not the type to do a harem either. Romance wise for the 3 FMCs, this is a doomed premise to start with.
Personally, as a degemerate I'd prefer a harem ending, as impossible as that may be. Or at least, that he end up with Elsa.
Also, they could be as rude as they want to the queen imo. She literally said the entire kingdom relies on the three of them, and that if they were to even be down in the dumps, that it would affect the morale of the entire kingdom. Sounds like to me that they're more important than the royalty when it comes to actual influence lol