Prior to the events of the movie, they were a alligator and mosquito that Krank experimented on to turn into humans and they thought of him as their father. Later, they were sent to animal control after the animal control cops found out the results of Krank's experiments.
They were seen when Krank was trying to get them to destroy the machine, they denied him to do it.
When Krank turns Spot into a man, he orders them to come and help him make plans for his 2 year world tour. After Ian frees them, they're ordered to find Spot and Leonard.
While on the way to Spot and Leonard, they reveal their true potential and hate being minions.
After Krank is turned into a mouse and Spot is turned back to a dog, Jolly eats Krank and Ian to to take care of them. They seem to be having a better life.