Is it possible 1) to read two Surah in one Raka'h of Salah? 2) To read only one Surah in all the Raka'h of Salah i.e. same Surah in all the Raka'h of Fajr, 1st two Raka'h of Thuhr and others? 3) To read a Surah during the last 2 Raka'h of Thuhr, Asr, Ishaa and last Raka'h of Maghrib?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.

It is permissible to recite two chapters in one Rak'ah after reciting Al-Faatihah (the opening chapter of the Quran); Al-Bukhari wrote a chapter entitled: "Combining two chapters in one Rak'ah". He narrated the story of the man who used to recite chapter 112 (i.e. chapter Al-Ikhlaas) before reciting another chapter, and the Prophet confirmed his act. However, it is better if he recites only one chapter, as this is what is confirmed from the Prophet .  

There is no harm also in reciting the same chapter in both Rak'as, indeed the Prophet recited chapter 99 in the first and second Rak'as of Fajr, as reported by Abu Daawood; but he usually recited a different chapter in the second Rak'ah, and this is better.

Finally, it should be noted that it is permissible to recite another chapter after Al-Faatihah in the third Rak'ah in Maghrib prayer and in the third and fourth Rak'as in Thuhr, 'Asr and 'Ishaa' prayers. It is confirmed that the Prophet did so, but he usually recited Faatihah only in the third and forth Rak'ah, and this is the best.

For more details, please refer to Fataawa 86915, 84995 and 83389.  

Allaah Knows best.