Hi fitspat,
Start by clearing off all of your pending invitations and start with one player a time. Ask that player to clear off any pending invites in their email if they have any.
Visit your friend's profile and send a country club invitation by clicking the invite to club button at the top of their profile. This will send an invitation to the email they entered when they registered on WGT. After you send the invitation ask them to check their email and look for the invitation from you. Once they receive the invitation they must log in to WGT first and then click the confirmation link in the email. If they are not logged in first (or auto-logged in) it will not work.
If your friend does not receive the email invitation ask them to double-check the email listed in their account information is correct and there are no typos. Have them check their Spam/Junk folders as well just in case it's being redirected to one of those folders. CC invites are working properly and most problems are a result of incorrect emails or the player not being logged when they try to accept the invite.
Slowly work through the people you wish to invite one at a time until you are more comfortable with the process. It's only 3 steps, so you'll warm up to it pretty quick.
Good Luck =)