They are fish that appear to be conjoined twins sharing only one body. In the movie, their pants and shirt are in dull green and their body color is peach. One twin has a beard and the other one is balding. They also wear black boots. In the video game and book, their appearance is slightly different - their skin and shorts are dark green while their shirt and shoes are pansy purple.
They are seen in the scene where Victor is walking around with the Goofy Goober theme playing, to see who the "baby" was. The twins then both say "Goofy goofy goobers goobers yeah!" and they shut their mouths, before Victor deals with them.