any bookings for above 6 people are done in prs/booking office only and you can very well request to give adjacent seats/berths. in a very recent booking, 15 students went in two adjacent bays (8+8). similarly, they have been booked for their return also in the same pattern. so if you have more than 6 persons in a group, you have to go to the counters only. if you book thru irctc, it is bound to split. more than 6 persons are considered as group booking and cannot be done in irctc.