I'm not sure what you mean by crowsfeet attachment. If you are talking about the endings of the lines connecting to the fields in each related table, that is merely showing the connection.
All relationships have the potential to be a many to many relationship. In your case, even though a Zipcode can belong to several Members, if a Member has two or more homes, they could belong to several Zipcodes.
If you set validation of the ZIPCODE field in Zipcodes to 'Unique', Filemaker will adjust the graph for you.