My question is now a days in islam many sects presents quran and sahih hadith to prove their sects are on stright path. so is it mean that only quran and sahih hadith or manhaj e salaf is must to know the stright path ?

The straight path is the way of tawheed and following the Prophet salla Allahu alaihi wa sallam.
People’s commitment varies and it doesn’t mean that those who are a bit lax are not out of the straight path but they are not fully in it.
Therefore, try your best to follow the Quran and sunnah by the understanding of the salaf.

Please visit here for detailed fatwa information directly from highly respected scholar