Is there 2 Rak'ahs Shaf' and I for Witr after Isha prayer or is it ok to pray 2 Rak'ahs Sunnah after Isha and then 1 for Witr instead of 2 Sunnah, 2 Shaf' and 1 Witr. Please explain the matter in some detail.

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

1) The time of Witr prayer starts from after 'Isha prayer and continues until the break of dawn.

It is valid to perform one Rak'ah of Witr, three, five, seven, nine or eleven Rak'ahs.

Abu Ayoob al-Ansari narrated that the Prophet said: "Whoever likes to perform five Rak'ahs of Witr, let him do so; whoever likes to perform three Rak'ahs of Witr, let him do so; whoever likes to perform one Rak'ah of Witr, let him do so." [Abu Daawood, an-Nasaa’i, Ibn Maajah]

As for the Sunnah of 'Isha prayer, it is different from the two Rak'ahs of al-Shaf`i, which are performed before the last Rak'ah of the late night prayer.

For more benefit, please refer to Fatwa 39577, 83303, 84482, 92197, 92752, 98754, and 351082.

Allah knows best.