Many types of the more common eels sold in the trade can be housed together providing they have the appropriate room to grow and feel comfortable. In many cases they will actually share the same burrows as they become comfortable with one another.
Although eels are not that active unless it's time to fed, they still need a fair size tank to both accomodate their large adult sizes but also their large appetites. They create alot of waste and I would not recommend two in much less than a 150 gal
tank. If this is for your future planned 240 gal
, you should be fine. Just be aware that most inverts will not be possible, including larger snails. The can also be clumbsy around sensitive LPS