[Keyclenef]

1. Al-Hasan did not agree with apointing Yazid as his successor, in fact, Al-Hasan passed away before Mu'awiyah. According to some narrations it also went against the explicit treaty agreed to by Al-Hasan and Mu'awiyah.

Are you sure Hasan didn't agree? Also, why did Muawiyah (ra) decide to appoint Yazid as his successor when this would clearly turn the khilafa into a dynasty? This was the whole reason for the Karbala, if Mauwiyah (ra) never appointed yazid as his successor, then Karbala would not have happened. So why did muawiyah (ra) do it?

2. There are, as far as I know, no authentic narrations that Al-Hasan was poisoned at the order of Mu'awiyah. However, many Ulama of Ahl al-Sunnah lean towards believing in the narrations implicating Yazid, rather than his father.

So some ulema believe yazid ordered the poisoning of Hasan? Why would yazid do this when Hasan (ra) did not even oppose him, rather Husain (ra) did.

3. Talha and Zubayr both decided to leave the battle field, as they were reminded of the Prophetic ahadith that Ali ibn Abi Talib will be on Haqq, etc. Zubayr was killed by Amr ibn Jurmuz after having left the battlefield, and Talha was shot by Marwan ibn al-Hakam.

This makes more sense,