who is sachin and who is vashnu?

ok guys i know archana's sister kidnapped archana and manav's son. but i want to who is sachin who lives in manav's house and who is new bad guy vashnu as they call him in the villiage? i am confused guys please explain to me who is this new guy and who is sachin. i like pavitra rishta i watched everday. comments please.

Sachin is the son of Manav's elder brother and Shravani. When Manav's older brother died, Shravani and Manav married. They married so Shravani would not have to carry the burdens of a single mother. However, this relationship would not last because Manav really loved Archana. Manav and Shravani broke up and Archana-Manav got married. Before leaving the for the U.S., Shravani left Sachin with Archana and Manav. After the 18 year leap, we see Sachin has become a successful lawyer.