Who are the Muldoons (meaning an odd family) and where is this expression from?

I can give most of this. They were a real family in Ireland who caused a lot of trouble locally and became synonymous with troublemakers. Somehow the name was reversed to Noodlum which again shifted to the current term Hoodlum. The same is the derivation of hooligan except that never varied from the actual name.

There is a different explanation in Wikipedia ), it originated in San Francisco in the mid to late 19th century from a local newspaper's rendering of a gang's call to fight, i.e. "huddle 'em".
Here are all 5 possibilities

http://sfist.com/2007/05/25/welcome_to_sfis.php
But all that means is it isn't 100% certain, unlike Hooligan which is a direct correlation with its origin.