Cant notify all users

I have spreadsheets set up and I'm the owner. When I make changes I can select 'share' and 'notify shared users' to let them know there is a change.

However, when a member of the group makes a change, they go to the 'share' menu and all they have is 'notify author'. How can they send a notification to all shared users (i.e. the others in the group) and not just to the author?

A colleague of mine has this working on his spreadsheet and we're racking our brains tryign to figure out why this isn't working.

Thanks, Rich