there are two alternatives - 1. go to any reservation centre and ask for bulk booking counter (more than 6 persons) and book your ticket.
2. if you have a log in id and passwrd in irctc website - you can book 6 tkts at a time and another 2 again. the chances of booking in the same sequence/compartment are 50:50. If there are sufficient number of berths vacant on ur travel date, they may get in the same coach. if not it may be scattered in two coaches. if there are two families of 4 persons each, better way is to book 4 tickts at a time (or as per family - yr choice so that at least the family does...
more... not get split.) you can always adjust with other co passengers during joureney time.
i have told both possibilities - choose your convenient way and do the booking. thanks