Deleting relationships is difficult, often impossible for managers without a Pro subscription. Sometimes you even need to be a curator.
If you post your request in https://www.geni.com/discussions/216411 then a curator will help. Best is to describe the issue including a link/url (copy from the top address bar of a profile).
If you prefer you, you could post it here and I'll have a look but my permissions are the same as you, but I can have a look to see if you could do it yourself.