If a person arrives at a place and finds people praying the Isha prayer and they are in the last rak'ah, and he joins them while they are reciting Al-Fatiha, how should he complete the prayer in detail? For example, when they sit for the final tashahhud, should he recite the tashahhud and the Ibrahimic prayer? And when they finish and he stands to complete the prayer, should he recite aloud, and should he recite any surahs after Al-Fatiha?