Nalla,
If I am understanding you correctly, you will have to do a PQR and then qualify your welders to that. Single side CJP's with no backing are not pre-qualified. PQR (with first welder qualified when tests pass), WPS from the PQR test report, then qualify more welders to the new WPS.
IF the plate were with backing, then yes, your 3G and/or 4G welders would be qualified to run the 1G position. But not without backing. That changes everything.
Have a Great Day, Brent