Little late to the party....
The trouble I've had with eels is matching them up, and giving them enough territory. The trick I've found is to get them small and let them grow up together. Some of the larger eels (like green morays and tesselatas) don't look like they need much space, but become very active at night (and will actively eat your fish population despite any regular feedings).
I've had three greens get along well in a relatively small area, then tried to transition those same three into a MASSIVE aquarium only to have them fight until one died.
The last two I kept were a large Tesselata and a Giant Moray (Gymnothorax javanicus). They would eat from us, then at night would still eat the 'filler fish' in the tank from time to time. I don't have great pics of them...
In this pic I was just trying to get the two patterns to compare them. The Tessalata is in the back/left.
Here's me with one of my old green morays. Gives you an idea of how big the aquarium was we moved them into.