Yup, I think things would probably be a little awkward between all three of them for a while. "Sorry, I didn't mean to sleep with your brother!"
Actually, upon reading how you frame it, it occurs to me that it's not at all clear to me what the brother actually thought about his brother's sexuality. We know he was sneering about it and being provocative, but we don't know why.
It's possible he was straightforwardly revolted, and trying to cope with the fact that he never came to terms with it. Or, it's possible he already knows he's also gay(/bi/whatever), but has doubts about himself and is projecting that onto his more openly gay brother, or else maybe he's upset because his brother went off to be gay and now he feels he has to be the "normal" one.
Hell, maybe he's just jealous—if Kageyama partially cut ties with his family, it could be frustrating to meet the people he stuck with instead. Or, he could even be drowning in rage at how the world treated his brother, and by testing Hiura with provocations, trying to get the world to show its true ugly colours, so he can stay swaddled in loathing rather than face whatever feelings threaten to overtake him if he stops and stands still.
Well, to some extent I get that this has to be ambiguous to allow the other mysteries and ambiguities, but still.