I have booked four person ticket of 3rd ac in one PNR number. Now I want to cancel two person ticket from them. Are the remaining two person tickets on same reservation valid or not?
Yes you can cancel tickets of passengers individually.
Login to your IRCTC account select booked history select the appropriate ticket then you can select check boxes side to the name of passengers and select Cancel ticket this thing only cancels particular ticket of that passengers and remaining tickets will be alive.