There are several previous discussions on using Rsync to copy from one My Cloud to another that can be found using the subforum search feature, magnifying glass icon upper right. Here is one such discussion:
https://community.wd.com/t/success-3-rsync-backup-between-my-cloud-devices/93945
Currently I belive that the SSH access is confined to the “root” account. One would most likely have to edit the SSH config file to allow for more users/accounts. Again there are several discussions on this issue that can be found using the forum search feature. Here is one such discussion (see the posts near the end):
