This following KB will address the creation of a column within the same hierarchy and the naming conventions that should be followed to further prevent confusion when troubleshooting.
First off, a sibling and cousin table can have the same element or column name but a parent and child cannot. (See the diagram below)
Sibling and cousin tables are not directly related, and therefore are allowed to have the same element/column name.
(ServiceNow does not recommend using column names between sibling or cousin tables, but if it is absolutely necessary it is recommended to use naming conventions that will allow users/admins to distinguish between the columns respective to what table the columns live on)