You want to add new cameras to replace the original ones on the same Crystal and the IP address/port/username/password of the new cameras should be synchronized the same as the original ones.
1) Set the IP address/port/username/password of the new cameras the same as the original ones.
(2) Replace the IP cameras physically.
(3) Go to Config > Recording server > device list, and click auto detect for each camera. (or manually select brand/model for each camera).
(4) Commit the changes.
(5) Regarding multi-stream setting, you could configure one camera, and then copy it to the other cameras if they are of the same brand/model. Please find the "copy to" button shown in the image below: