There are a few sites online that provides you with mock tests of SNAP such as Crack, MBA universe etc. which can be very helpful and I would recommend to take a few other MBA entrance mocks which are available as they follow almost same kind of pattern.
Yes, While filling up the form you need to select the colleges you are interested in. There is common exam and score for all Symboisis colleges. But the pattern of GD PI may differ. So register for the course you wish to pursue and fees structure also varies according to the course you select.