With Dialer Video Desktop in beta release, we are working hard to incorporate all the features you want. Unlike the mobile apps, there is not (yet) an "Add third party" button, but it is still easy to invite one ore more people into your Dialer Video call on desktop. Just share the call URL with the third party, by email or text message. You can copy the link from one of two places:
1. The call link appears in your waiting room queue.
2. Once you are on the call, it is the URL in browser