I would be surprised if someone accepted Pena/Casilla for Napoli. Pena has a track record of power, poor average, and inconsistency. It is very unlikely he has changed. Casilla, though a solid arm, isn't necessarily destined long term to hang onto that job. They're both iffy pieces. Napoli, despite the average, has proven he could have a fantastic season. He's a top 3 catcher as well no matter how he's started.
If Napoli only had 1-2 HR and that bad average, then he could conceivably be worth those two guys. But he's still got the power and will likely bring that average up, so no, it's not that fair of a trade.