It seems the elder Kawamotos all have a newfound understanding of Rei. They're well aware of how he feels and thinks, now. Grandpa always knew he was a tough kid, thanks to his Shogi, but he didn't often show it outside of the Shogi board.
But he's had more and more times where Kiriyama, Captain of Rokugatsu-tou, can show his quality (to paraphrase a LotR line).
I said previously that I don't think they are necessarily opposed to him having a relationship with her, but... timing is important, also proper pacing, my boy. You don't just pull that when you haven't even given her a confession yet. She'll be aware of his true feelings in time, though. And she won't be able to deny them, or her own, when that time comes.
It was a good weapon against the father, though, to be sure.