Yes, by using SFTP and setting up groups you can traverse directories within other user folders by implementing virtual directory links.
If you require multiple access for the lifetime of the domain, then by far the simplest method is to create a "shared" user, create a folder in it's account, and remap that directory from the website using Domains > Remap Sub-Dir. Then just give the relevant people the username/pass for access.
If you only require access to set the website up initially, just use the owners SFTP credentials. They can change their password to something arbitrary, let you upload/edit the site, then change the password back when you're done.
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