1. When viewing pending members, you should be able to remove an invitation by clicking the Gear icon under the Actions column. If you chose the option to pre-create the login, then there is no invitation and the user is already member of the organization. They would appear in the Current Members list and can be removed.
2. Disabled users are still members of the organization and consume 1 user spot. The purpose for disabling a member is to prevent usage on that account. For example, if someone quits your organization, you can disable the user until you are able to reassign any items or groups they own. The, once you've cleared out their content, you can delete the user.
Thanks,
Mike