Hola. Hay posibilidad que ambos sitios compartan la base de datos? Si es así, podés usar la clase
wpdb.
Cita: The $wpdb object can talk to any number of tables, but only one database: the WordPress database. In the rare case you need to connect to another database, you will have to instantiate your own object from the wpdb class with the appropriate connection details. For extremely complicated setups with many databases, consider using
hyperdb instead.