A family of Microsoft word processing software products for creating web, email, and print documents.
Sorry, it's not possible to use a relative path to the attached template.
Instead, consider using Office's Workgroup Templates feature that allows you to create a template folder on a network share. Then every user has the same path to the template. Here's how to set up Workgroup Templates: Shared Workgroup Templates - Best Practices
BTW, except for special circumstances, you should leave the Automatically update document styles option unchecked, it can cause unwanted formatting changes