Oracle SQL Developer: Copy paste tables, with 2 different instances, with different table structure
"However, the tables in the DEV keeps adding/changing, which is why when I run the query, it hit the error saying the table/view does not exist."

Short of putting a lock on every object in the remote database during your copy, I'm not sure this is avoidable. In truth your approach this is unneccessarily complicated. If you want to clone your DB, use the existing cloning tools. There's no need to reinvent the wheel for this application. I'd suggest using datapump to export/import your schema if you want a consistent snapshot.