What is the ruling on the prayer of the Imam and the congregants if the Imam errs in the first Tashahhud and the sitting for the Tashahhud, and if the Imam's prayer is invalid, must the congregant ask him to repeat it, and how does a Muslim intend to repeat a prayer if it was invalidated and he does not remember which prayer it was?

Alerting the Imam by saying "Subhanallah" (Glory be to Allah) is obligatory if he omits the first sitting for the Tashahhud (definition) or if he sits in the third Rak'ah. Your Imam omitted the first Tashahhud and added a sitting after the third Rak'ah and stood for a fifth; therefore, he must perform the prostration of forgetfulness (Sujud (definition) al-Sahw) before the Taslim (definition) (salutation). If he does not perform the prostration of forgetfulness, his prayer is valid according to some scholars, and so is your prayer. Whoever's prayer becomes invalid and he does not know which one, he must pray all five daily prayers. There is no re-prayer for you or your Imam, but it is obligatory to learn the rulings of prayer.