I think you're making your standpoint harder to understand, though since we kinda discussed this before I already know your argument, but simply put,...The one that Sera talked to on phone in the Ramen case is her middle-bro shuukich...!
BUT, the one that has been helping her with the past cases and that also recognised conan in the "bowling" case is her older brother shuichi!
Shuukichi recognising Conan's intelligence indicates that he might've met him in the past, possibly with Sera and Mary.
One thing to note is that when Sera wondered how her bro knew conan in the "bowling" case(which indicates that the bro should not have met him before according to Sera), she got a text from him and reacted as if he explained everything to her, then we get the wizard thing! Point is, wizard sentence was a P.S, so it doesn't have to relate to their convo about conan, so he could've simply asked sera whether she's met the person she came to look for in Japan(meaning that the bro might not know the "wizard" is the same boy they were talking about a minute ago, indicating that the bro might not be mid-bro shuukichi[who might've met the "wizard" with sera and mary] but rather old-bro shuichi)... just a thing to consider...