Yes, Fly Hard is a play on the Bruce Willis movie, Die Hard, and the plot of the episode is a 'homage' to the events of the movie.
Barbarians at the Planet is, I believe, a play on the phrase Barbarians at the Gates. I'm not entirely up on the origins of the phrase, but I think it's generally believed to go back to Roman times. Perhaps even to the historical sacking of Rome by...well, the barbarians. <g>
These days though, its generally used to denote circumstances where the victims of a catastrophic event are watching things unfold but can do nothing to stop it or help themselves.
As far as Clark, Lois and the rest of the Planet staff are concerned, I think Luthor - the true barbarian who has no appreciation of a free press which doesn't do his bidding and who seeks to destroy it - taking over the Planet probably qualifies on that score.
So I think the titles fit the episodes pretty well.
LabRat