How should a son deal with his Sufi parents who threaten to disown and ostracize him? Is it permissible to argue with them and conceal his Salafi methodology from them? What should he do if he is forced to attend innovations like Mawlids?

All praise is due to Allah for the blessing of repentance and for knowing the sound creed. Strive to remain steadfast upon it by acquiring beneficial knowledge, performing righteous deeds, and associating with the righteous.

It is advisable to be patient, gentle, and deal kindly with family, especially parents, as this has an impact on influencing them, in accordance with the Almighty's saying: "Repel evil with that which is better." You may debate with them if you possess knowledge that refutes misconceptions; otherwise, you should turn away or seek assistance from someone who is knowledgeable and capable of da'wah (invitation to Islam).

It is not permissible to participate with family in innovations (bid'ah) and misguided practices. You must find any possible stratagem to avoid going to them.

Under the designation of Ahl al-Sunnah wal-Jama'ah falls everyone who follows their methodology, regardless of their affiliation with a specific group.