If Yokiko joins the band, it's gonna be a bloodbath.
And yeah, I understand where he's coming from: his step mother doesn't know what he likes or not, Chiaki isn't there anymore. His stepbrother is nice but is much younger and has no blood relation to him... his father is never at home. It's understandable he feels awkward and like a stranger in that home. Even more-so that his father probably looks down on his music career and doesn't really know how to interact with him, since he basically didn't raise him and has always been a distant father that piled up his expectations on Chiaki (which led Chiaki to run away).
So, I think it's normal he takes his distances with his "family".