Sunan-e-Muakkadah

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?

Sunnat Salaah before zuhr

Q: I would like to ask concerning about the 4 raka'at sunnah before zuhr. I heard someone say that there should only be one salaam in the entire 4 raka'at. Then someone told me that there should be 2 salaams, now I'm confused. Which one is correct? or it depends on which madhhab I follow? Please elaborate.