IF the brother pair Kaguya with Mikado, he still cares for his imouto in his own way...
but if the groom candidate is some old ass rich dude/politician.... than he's the type of 1% scum you can find IRL....
at least if it's Mikado, officially he'll be Miyuki's rival again, but if they've become bros, well, I can see Mikado supporting the two.