[Do not dub me shapka broham]

I'm going to rely upon the experts here, but I believe that Scrooge McDuck was Donald's Scottish cousin, who was responsible for raising Huey, Dewey and Louie after Donald was shipped out overseas.

[netmilsmom]

This is what I find on the triplets.....

http://duckman.pettho.com/characters/hdl.html

They are the children of Donald's sister Della and an unknown father.

[tiamat]

I thought he was an Uncle?

Doesn't matter.