Q: when attempting to set up family sharing i get 'You cannot send an invitation to your own account.'

Why would you possibly want to send an invitation to yourself. Once you have set up family sharing you are already included in that sharing set up.

Then you are following the wrong process somewhere along the line, start again do make sure you invite your family and not yourself.

I have family sharing set up.

If the person you are inviting is using your ID you will have problems.

Someone else shouldn't be using your ID, you need to sort that out before you do anything else.

I Had the same problem.  I didn't realize my wife was added to my account as an alternate email address.   I deleted her email from the main account and it fixed the problem.