Eventually, your current three will become two when a pair forms. You will then have to remove the odd man out or it will be banished to a corner of your tank (best case scenario) or killed.
Also, if you still have a snowflake eel in this tank, none of these little clowns has great survival odds in the long run.
Properly housed, clowns can easily survive in captivity for a decade or more. You'll have a better chance of enjoying them for a long time if you stick with a pair and set them up in a different tank.