The marriage isnt a real one na. They havet taken any vow infront of God na. As Sia said today, its useless to send him behind the bars for a day or two. To give V his due punishment, they need strong proof n to get the proof, they need time. This fake marriage is mainly to get time.
If Gayatri n the whole fam will get to kno abt V then V will b thrown out of the mansion n wont let RaghaVi to get any proof.