Thank you for the pointer.
To get it working I did the following:-
1) NAME-RelatedAddress1,TYPE-Address,EXISTING-RelatedAddress2
2) NAME-RelatedAddress2,TYPE-Address,EXISTING-RelatedAddress3
3) RULE- If Address.RelatedAddress2 WAS CHANGED Then
Address.RelatedAddress1=Address.RelatedAddress2
The above works great but when I delete a related entry on one address it doesn't remove it on the other automatically. Is the Rule incorrect?
Thanks