When creating a relationship between two tables that have an Attribute with the same name, the Attribute is created twice in the child table.
Rename the Attribute in the child table to another name.
Use the Foreign Key Mapping feature to assign the Foreign Key to the correct Attribute - please refer to the Help file for further information on how to do this.
Enhancement request CR 85440 has been submitted to Development for consideration in a future release of Toad Data Modeler. A popup will be displayed offering customers the option to either map or rename the Attribute in case it shares the same name between the two tables.
Please review the following video for instructions on Foreign Key Mapping