It is possible to use WhatsApp to hold videoconferences, but calls are still limited to four people and can only be made via mobile phone.
To start a group call, open the group's chat tab and tap the call icon in the upper right corner of the screen. Once your contacts list launches, choose the person that you want to add to the call. You can add up to three people to your call. Then, click the camera icon
To add people who are not in the group, select a contact and open the chat tab. Tap the camera icon in the upper right corner of the screen. Once the call gets connected, check for "Add person," which looks like a small figure with a "+" sign in the upper-right hand corner of the screen.