The "Real Life Carl and Ellie Fredrickson" is a reference to the four people who greatly inspired the creators of UP.
The credits read:
dedicated to the real life carl and ellie fredricksons [note the "S" on the end] who inspired us to create our own adventure books
Joe Grant Ralph "Papa" Lopez Mike Oznowicz Alice Davis
You just have to zoom WAY in on the end credits to read it all! lol
Hope this helps. -Trillo333- III
Some of the men who inspired the character of Carl include: Joe Grant, a Disney animator who worked on “Snow White and the Seven Dwarfs” in the 1930s, and Mike Oznowicz, father of Frank Oz, of Muppet fame, who presided as president of the Puppeteers of America.
Alice Estes Davis (born 1929) is an American costume designer. She is most famous for her work with Walt Disney, who employed her to develop costumes for films, television, and theme parks.