You can use the Low Rise Medium Density Housing Code from 1st July 2020 to check whether your proposal is complying development.
A Complying Development Certificate may be issued for your Dual Occupancy for land zoned R1, R2, R3, or RU5 if the proposal meets all of the relevant development standards. You can check your zoning on the NSW Planning portal spatial viewer.
If your proposal does not meet all of the standards you must lodge a Development Application.