Is there any way that a viewer can mention other team members except the team member that invite the veiwer?

Here is the situation.

There are 5 people. A,B,C,D and Z.

A,B,C,D are team members of one project.

A invites Z in this project just for a viewer.

Now Z only can mention A when leave a comment.

Is there any way that Z can mention B,C,D in this project?