Hello Kok,
The OS user are manage locally i presume, please remove the saphostagent on the host that you want to add, clean up the the /usr/sap/hostagent folder.
Also check if the <sidadm> exist on the additional host, if yes remove it.
Once the check done, from the host you wants to add go to the /hana/shared/TDB/global/hdb/install/bin and run the ./hdbaddhost script with the root user.
Please let know the result
Williams