Is AES-256 over AES-128 weakening the original encryption?
Obviously, as long as the AES-128 (TLS) channel is keyed independently from the AES-256 (file encryption), the TLS encryption cannot damage the file encryption.

Let us consider what would be true if it could.  If that somehow did weaken the file encryption, this would allow this attack on an encrypted file – he could take that encrypted file, and send it through his own encrypted TLS link.  He can then use the records from that encrypted link, and exploit the weakness to attack the file encryption.

Since he can do that, any weakness that would apply to the combination would also apply to the file encryption alone.  We don't believe that there's anything wrong with the file encryption (assuming that the AES-256 key is randomly chosen), hence there isn't anything wrong with the combination.