You are implying to make request to IR , when you say 'can i request to change in same coach' ?
No you can not request IR now. This could have been done at the time of booking tickets to PRS window clerk. OR taken care at the time of making e.ticket.
When you board the train, you have option to request your copassengers to help you to change mutually, with information to TTE, as he is searching for some loopholes such as 'passenger on found on seat', and allot to others....
more...
So till your tickets are verified by TTE , ensure that you and family memebrs stay at seats allotted. and after checking, move away.