Hi Basu,
I am not sure if there is VFS office in Kolkatta, but I applied in VFS New Delhi office in March 08. The link is
http://www.vfs-ch-in.com/
After getting all my permit papers from canton, I applied there and got visa stamped in two days. They did not did any background verification for me, as I was coming alone. But yes, I think for dependant they will do the checking.
hope this helps.