Witr and Nawaafil

Masbooq in witr salaah of Ramadhaan

Q:

1. In Witr Salaah in the month of Ramadhan, if the masbooq joins the Imam in the ruku of the last rakat, is it wajib for the masbooq to recite dua e qunoot when he stands up to complete his missed rakat and in which rakat will he recite dua e qunoot?

2. In Witr Salaah, if the masbooq missed all the rakaats and did not recite dua e qunoot when he stood up to complete his Salaah, is it compulsory upon him to repeat the Witr Salaah after the Salaah time has expired?

3a. If the masbooq turned for salaam with the Imam accidentally or not knowing the masala and he did sajdah sahw at the end, is the Salaah valid?

3b. In the above situation, if he didn't do sajdah sahw, is it compulsory to repeat the Salaah when the Salaah time has expired or is the Salaah valid but incomplete?

4a. When the Imam did salaam to do sajdah sahw, the masbooq accidentally or not knowing the masala, he also turned his head for salaam and then did sajdah sahw at the end of the Salaah, is the Salaah valid?

4b. In the above situation, if he didn't do sajdah sahw, is it compulsory to repeat the Salaah when the Salaah time has expired or is the Salaah valid but incomplete?

Performing two rakaats sunnat before zuhr due to the fardh salaah commencing

Q: I was offering the four rakat sunnat before zuhr in the mosque. I was offering the second rakat when the iqaamat started, so I completed my salah like a two rakah prayer to join the jamaat. Will I have to offer the sunnat again after zuhr or is it permissible to skip it? And also should I do sajdah sahw when I repeat the sunnah to after the jamaat?