Donald's Nephews
Donald's Nephews (1938) is a Donald Duck animated cartoon which features Donald being visited by his three nephews, Huey, Dewey, and Louie. This cartoon is Huey, Dewey, and Louie's very first appearance in animation. The short, and the three nephews, was the idea of Al Taliaferro, the artist for the "Silly Symphonies" comic strip, which featured Donald Duck. The Walt Disney Productions Story Dept. on February 5, 1937, sent Taliaferro a memo recognizing him as the source of the idea for the planned short. Taliaferro subsequently introduced the nephews in his comic strip, which by this time had been renamed "Donald Duck", on Sunday, October 17, 1937, beating the theatrical release of "Donald's Nephews" by almost six months.
Ludwig Von Drake
In the story "The Family Tree Spree", Donald scares of seeing Ludwig's specs on the floor and thinks about them as "Uncle Ludwig's specs". In the end of this same story, it's revealed that Ludwig also appears in Donald's paternal family tree, wherein he and Donald both have an ancestor called Colombust Duck. Since Humperdink Duck (aka Grandpa Duck), Grandma Duck's deceased husband, was probably almost contemporary with Ludwig Von Drake, it's possible to consider they were half-brothers, Donald being thus Ludwig's grandnephew. Ludwig revealed in "Blown Up Genius" that he came from a long line of glass blowers. In "The Big Payoff", it's revealed that he spent many months living in Donald's house since his arrival in Duckburg. Ludwig wins a TV chess challenge in this comic story, making Donald exclaim, "Yippee! He did it! Now he can pay all he's owed us (he and his nephews) for these many months!". According to the story "The Jewels of Skull Rock", Ludwig spent six months in Donald's house.