How can five tashahhuds be combined in the prayer of a present ma'mum if he catches the second rak'ah of a traveling imam's prayer, and what is the authenticity of there being a tashahhud after the sajdat al-sahw according to the fatwas of the majority of scholars?

The jurisprudential issue concerns the trailing of a resident behind a traveler. You mentioned that the Malikis are of the view that a latecomer (masbuq) who catches one rak'ah with the traveling imam should, after the imam's salutation, perform four rak'ahs: The first with only Al-Fatihah, followed by sitting for the tashahhud. The second with only Al-Fatihah, followed by sitting for the tashahhud. The third with Al-Fatihah and a surah, either audibly or silently, followed by sitting for the tashahhud and then performing the salutation, along with two prostrations of forgetfulness (sajdatay al-sahw) if forgetfulness occurred. This would make a total of five tashahhuds. It is also noted that the Malikis prefer the tashahhud before the salutation from the prostrations of forgetfulness.