Method of Salaah

Reciting a longer Surah in the second rakaat

Q: Assuming in the first rakaat of witr, one recites Surah Lahab and Surah Ikhlaas in the second rakaat. Is it necessary to make sajda sahu as only Surah Falak or Surah Naas can be recited in the third rakaat but these Surahs are longer than Surah Ikhlaas. Likewise, in any other namaaz, if one recited a Surah in the second rakaat that is slightly or much longer than the surah recited in the first rakaat, what is the ruling?

Dua after Salaah

Q: In Nizamuddin markaz we have seen that the Imam saheb does not make dua after salah with congregation and we make dua individually but in other masaajid the imam makes very short dua with congregation. Which one is sunnat?