What are the differences between team observers and contributors?
Team observers are more like guests to your team. They have view-only access, and can't post updates to your team's feeds. However, they can comment on and see the full activity of any feeds that you invite them to.
Team members are your regular team members. They have full access to the feeds that they are a part of. Members can also create new feeds in the team scope, and invite team members to participate. However, they cannot invite people who are outside the team.