Yes. If you miss any part of the action, it will be available on-demand using the same watch link.
Yes, you may share the registration link with anyone who you think may benefit from this event.
Please check the bottom left hand corner of the YouTube video to see if you may have accidentally muted yourself. YouTube remembers the last setting for your volume when you previously watched a Youtube video.
Try refreshing or reloading the page to see if it works, or if you have other too many applications or other video windows open, try closing them. If the issue persists, open up YouTube on another browser and check if you can view other YouTube videos. If you are not able to view other Youtube videos, this means there may be some issues with watching Youtube videos on your machine. If you are able to view other Youtube videos, this may mean that your machine is not able to watch videos that are live streamed.
Try updating the Quality settings on the Youtube controls near the bottom of the content window.