If I’m right about what I think is happening, this doesn’t really seem specific to Google Docs, but rather a workflow problem.
When you have a group mention (e.g. @staff) it gets baked with a link to the group’s URL. So what seems to be happening is they’re copying the rendered post instead of the post’s source.
Instead of doing so, they should copy the post source to avoid this happening.
A Discourse feature that may make sense for your use case is our “Shared Drafts” feature.