I believe you have to ignore those passages in Ephesians in order to make your belief work.
As for being seated with Christ:
Well, Jesus tells the twelve disciples that they will sit upon twelve thrones.
"And Jesus said unto them, Verily I say unto you, That ye which have followed me, in the regeneration when the Son of man shall sit in the throne of his glory, ye also shall sit upon twelve thrones, judging the twelve tribes of Israel." (
Matthew 19:28).
But we know Judas did not make it in the end.
For Judas later became unsaved because he committed suciide.
For the Scriptures say he fell by transgression.