Answer
(Fatwa: 442/417/N=1434)
(1) If lungi or pyjama is worn above underwear then it is lawful to offer salah with it without any doubt and that salah shall be valid provided no other thing is found which prevents salah from being acceptable.
(2) It is also not correct. If the muqtadi turns for salam after sitting equal to reciting tashahhud then too his fardh of salah shall be valid. However, it is makrooh tahrimi to do so without any excuse. The muqtadi should turn for salam along with the Imam. It is said in Rud al-Muhtar (Vol. 2, p. 240 published by Maktaba Zakariya Deoband):
قوله: “ولو أتمه الخ” : أي : لو أتم المؤتم التشهد بأن أسرع فيه وفرغ منه قبل إتمام إمامه فأتى بما يخرجه من الصلاة كسلام أو كلام أو قيام جاز أي : صحت صلاته لحصوله بعد تمام الأركان لأن الإمام وإن لم يكن أتم التشهد لكنه قعد قدره ……. اهـ
Allah (Subhana Wa Ta’ala) knows Best
Darul Ifta,
Darul Uloom Deoband