IN sitting first AC (day journey) like Shatabdi and Gomti, there is only chaircar. Gomti (I think) has only AC Chair car but Shatabdi has Executive Class (IAC confort) in addition to ac. chair car. There is nothing like a 2 seat coupe in these trains. If a 2 seat booking is made, you are likely to get adjoining seats...
Hope this is useful to you
thanks