And that stone was leading Uchiha to oblivion but like Itachi realized later on, the Uchiha could have been changed had he not went batshit crazy.
No, as they resisted negotiation. There was no "changing" an entire clan after years of tension. If you're referring to what he told Sasuke, he was saying that to give the boy confidence so he could move on in life. I guess the Uchiha were nuts, given they resisted a peaceful option and wanted to risk their lives like that.
He didnt have to take everyones life. He and Shisui together could have changed things through love of their clan. They loved Konoha more than their clan. Naruto would never give on Sasuke like Itachi gave up on his clan, thats why Itachi entrusted Sasuke to Naruto. Love.
Naruto wouldn't have given up since he's the chosen one and the ideal Kishimoto designated in the story. Itachi was the one in the Catch 22. And yes, going by the narrative he did need to take their lives as he didn't have an option in the first place. Itachi loved Konoha more than the clan... eh no. He just wanted to prevent further death and viewed the Uchiha as dead anyway.
Itachi and Shisui let themselves be used and tried to handle things alone. Had they been totally in synch with working together and actually stood up against the Danzo, the elders, their clan etc. The coup could still be mitigated.
Itachi stood up to his clan and was blown off (they're portrayed as the crazy ones) and killing Danzo/elders would give grounds for the Uchiha to be attacked right away. He's confirmed to have made the right decision in the story given his circumstances (whether you agree or not is an entirely different matter and not relevant to this thread). So, given that- no the coup could not be mitigated and the Uchiha/Konoha could simply not coexist.