In the light novel, Ayanokoji is clearly the more intelligent one. He has a unique ability to analyze situations and people's motives deeply. Ryuen often falls into Ayanokoji's traps because he doesn't fully understand Ayanokoji's true nature. Ayanokoji can anticipate Ryuen's moves and counter them effectively, while Ryuen struggles to keep up with Ayanokoji's complex thinking.
When Ayanokoji says 'I'll use any means necessary to achieve my goal', it reveals his somewhat ruthless side. He is not bound by conventional moralities when it comes to reaching his objectives. In the light novel, this could be a result of the cut - throat environment he is in. However, it also makes him a complex character as readers are left to question whether his actions are justifiable or not.
The Weasley family would be heartbroken. Molly would probably cry for days, seeing Harry as one of her own. Ginny, who had a crush on Harry, would be confused and hurt. She would try to talk to Harry and convince him to come back to the right side. Hagrid would be in disbelief. He had always been there for Harry and would find it hard to accept that Harry had joined Voldemort. He might even try to go after Harry on his own, without thinking of the consequences, just to bring him back to Hogwarts.
One of the notable quotes by Ayanokoji from the light novel could be 'I don't care about victory or defeat. What I want is absolute control.' This shows his unique mindset that is not focused on the typical goals of winning or losing but rather on having power and control over situations.
I don't know for sure. The ending of such a manga can be quite unpredictable and might not have been revealed yet. You could try discussing it with other fans to get their speculations.