The Sahaba by default are regarded as reliable, as Allah (SWT) has praised them for their dedications towards the Deen on numerous occasions in the Qu'ran.
No Hadith scholar since inception has said otherwise.
The sahaba who are thiqa by default should not remain thiqa by default if they commit fisq.
Then, I suppose we should throw all the narrations that have reached us through Shias (your ancestors interestingly enough) in the trash?
That rule only extends to narrators after the companions because their entire lifestyle needs to be examined, and scrutinised.
Allah (SWT) has divinely confirmed they are reliable in the Qur'an. This is the interpretation the entire orbit of Ahlus Sunnah extrapolate from the various verses.
You'll also come across statement from the students of the Sahaba, how many of them were at times reluctant to narrate Ahadith unless they could remember it word-for-word 100%. This is further indication, how they took great care in narrating Ahadith.