You will have to register for 2 GST states (2 registrations). Delhi & Haryana with the address of your rental property as business place.
Then charge CGST and SGST for both rental incomes and file 2 seperate returns for the 2 registrations.
Rental service cannot move accross states (like a CA services) nor can it be provided from your residence. (You cannot charge IGST). Your current service tax registration is also incorrect/incomplete as you may have mentioned only 1 rental address for both or your residence as business premises which is wrong. Most people followed this same mistake (since service tax was going to the central govt.) as you have done in the past. Kindly rectify it asap.
Regarding rates, it be 18% total -see attached file page 4 entry
36. All other services not specified elsewhere 18%With Full ITC
(please check if its 9% for CGST & 9% for SGST or something else & share the link or govt. notification)