Praying Witr Behind Those Who Split the Witr Prayer

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Tarāwīḥ is Sunnah Mu’akkadah and consists of 20 rakʿāt by the consensus of all four schools. Praying less than 20 does not fulfill the Sunnah Mu’akkadah, especially according to the Ḥanafī school.

If the people there are praying only 8 rakʿāt for Tarāwīḥ, then it is likely that they are Salafī/Wahhābī. In such a case, praying ṣalāh behind them is not permissible and is severely disliked, requiring a person to repeat the prayer (see al-Fatāwā al-Ridawiyyah, volume 6). 

As for the question about Witr, where they perform salām after two rakʿāt and then pray another rakʿat separately—a Ḥanafī’s Witr will not be fulfilled in this manner (see Radd al-Muhtār; al-Baḥr al-Raīq). 

Such a person should find a suitable Sunni Masjid for Tarāwīḥ. If that is not possible, then he should try to gather other Sunnis to pray privately together in congregation. If that is not possible, then he should pray alone, as Tarāwīḥ does not require congregation for the Sunnah Mu’akkadah to be fulfilled.