Coco (I) (2017)
Considering that surnames get lost with families having female descendants, as seen with Soccoro (Coco) and her daughters Elena and Victoria, this means that if Miguel's surname is Rivera, then the only way for Miguel to have the surname Rivera means that the surname comes from Miguel's grandfather, Franco.
It's a common fact in Mexico that towns have popular last names making it appear like everyone who lives in there are cousins. So, while the surname 'Rivera' may not be the most popular last name in Santa Cecilia, it's still common enough to provide three different families of Rivera's that form the overall Rivera family of shoemakers seen in the movie.
This means that following Mexican tradition with the surname of the father, followed by surname of the mother, it means that Coco, Enrique, Gloria and Berto all share the surname "Rivera Rivera".
Ernesto de la Cruz is the fifth character in a Pixar animated film to be revealed as the main antagonist in a surprising plot twist. The other four Pixar films to feature such a character are Toy Story 2 (1999) with Stinky Pete the Prospector, Monsters, Inc. (2001) with Henry J. Waternoose III, Up (2009) with Charles Muntz, and Cars 2 (2011) with Sir Miles Axelrod.