sir,as per rules,only confirmed passengers can board the train and the waitlisted passengers have to cancel their ticket...if one passenger(who has a confirmed berth)travels and other two dont,you have to get a certificate from tte stating that two passengers did not travel...you have to send it by post to irctc and file a tdr online for the same...if all 3 dont travel...simply file a tdr...full money minus rs.60+irctc charge will be refunded electronically back into your account from a period ranging from 3 days to 3 months...if all 3 travel,you will not be fined/detrained in practice,but it will cause inconvenience to you and your co-passengers