1)what if parents perform zinah,duty of son is what? 2)the way tabligh jamat is working, is it the way prophet (S) showed,please provide enough references from qur'an and hadith?

1) The son should in a polite manner bring their attention to the severity
of their sin. He should also make Dua for their guidance. If he feels that
it may be counterproductive to approach them directly, he should ask a
friend of theirs, or a respectable member of the community to approach them.
If this too appears to be counterproductive, then simply make Dua for them.
2) The principles on which the Tablighi Jamaat operate are to be found in
the Qur'aan and Sunnah. Please refer to the books 'Fazaa-il A'maal and
Hayaatus Sahaaba for details. Both are available in English.

and Allah Ta'ala Knows Best

Mufti Ebrahim Desai
FATWA DEPT.