See...
2AC has 52 x 3 = 156 berths.
of which, 95 is used in general quota, 30 in tatkal quota, 9 berths for RAC (18 RAC total), 6 berths as Lower berth quota, so you get 140 berths used up completely. Also 4 pax are above you, so in remaining 16 seats, 4 are taken by them (priority wise). Now in remaining 12 berths, you have to get 4 berths which now seems to be difficult as these will be used up by parliament/HO quota. So, CANCEL it and go for 3AC...