Just wanted to confirmed what Joachim mentioned.
No additional devices needed. I have video automatically loading on 4 x Echo Show 5 and 1 x Echo Show 8 simultaneously.
Make sure all devices have the latest firmware, including the latest apps on your phone. I relinked my Ring to my Amazon account and they all worked. Not sure if there may be other steps some users need, but this worked for me. I really appreaciate the button on the ring (muted microphone) which allows you to press the screenon the Echo Show to start the conversation.
Next request - a button which allows you to unlock / open your gate on the same screen and this would be PERFECT.
You can also find more information in this Community post.
Thanks again Amazon / Ring for bringing the first feature.
Bob