@fiesty76 if you tag a person with their @membername then they will receive an email notification. Have you had the opportunity to look at the Getting Started on Connect guide? There is a link in the left column of the footer on every Connect page that provides step by step "how to" for different tasks on Connect. Here's the direct link: https://connect.mayoclinic.org/get-started-on-connect/
The answer to your first question – … you will both see the post??? — we both should see your post (assuming we are following the discussion or you mentioned our @membernames. The answer to your second question – …you add a note to someone in the walking group who doesn't follow this thread, they won't see your response to them? — same answer, if they are following this discussion, they see the post or if you mention their @membername, they will see your note.