If the lionfish was bitten by your eel, your eel is likely suffering from starvation, particularly if it's a Chainlink......these are crustacean feediong specialists that need lots of shrimp and squid.
If your lionfish stung your ray, it tells me that you have too many fish in a tank that WAY too crowded.
I have an adult P. volitans lionfish, a 13" stonefish, 3 eels, 2 tangs, a 24" bamboo shark and a foxface in my 300 and nothing EVER gets stung....in fact, they often pilke up together as best friends.
Actually, I have 4 large lions and a pair of breeding fuzzy Dwarfs and have NEVER had a lionfish or scorpionfish sting another fish since I set up my first marine tank in 1969.
Mike