Praise be to Allah.
The answer to your question about al-sunan al-rawatib is a Hadith by the Prophet (may peace and blessings be upon him) in which he said:
"Allah will build a house in Heaven for whoever is diligent in observing 12 Sunnah Rak'at (as follows): 4 Rak'at before and 2 after the Zhuhr (Midday) Prayer, 2 after the Maghrib (Sunset Prayer), 2 after the ‘Isha (Evening) Prayer and 2 before the Fajr (Dawn) Prayer." (Hadith sahih narrated by at-Tirmidhi No. 379 and by others. Hadith No. 6183 in Sahih al-Jami’.)
Anbasah ibn Abi Sufyan quoted Umm Habibah as saying "Allah’s Messenger (may peace and blessings be upon him) said:
"A house will be built in Heaven for one who prays 12 Rak'at in a day and evening as follows: 4 Rak'at before and 2 after the Zhuhr Prayer, 2 after the Maghrib Prayer, 2 after the ‘Isha Prayer and 2 before the Fajr Prayer." (Narrated by at-Tirmidhi under No. 380. He said: The Hadith narrated by Anbasah quoting Umm Habibah in this chapter is a hassan and sahih hadith. It is under No. 6362 in Sahih al-Jami’.)
All the foregoing 4-Rak'ah voluntary prayers are to be prayed two at a time according to Imam ash-Shafi'i and Imam Ahmad.
Allah, the Exalted, knows best.