As far as I am aware, there is no multiple ownership. Each 'file' has one owner & one group associated with it. These are stored as the UID number & GID number from
/etc/passwd &
/etc/group respectively. If the 'file' is shared between servers and the names associated to the UID & GID do not match the it can be very confusing. Normal file permissions also include the global/other/world permissions.
You can, however. look at something called Access Control List (ACL) for each 'file' Within them, you can define more individual accounts or groups to have specific access, but there is still only one true owner.
Have a
read of this manual page to see if it helps.
I've used 'file' to refer to any object in the directory tree including files, directories, pipe, fifo, devices etc.
Kind regards,
Robin