Papa Nadachalla, or simply Nadachalla, is Papa Acachalla's fraternal twin brother who works as a vet. In the Gmod Star Wars Rancor Mod episode, Nadachalla came to register the new 'family dog' and give it its shots. What he found was a princess, who he then decided to flirt with. This enraged Gertrude to the point where she chased him out of the area, and he was forced to hide in some shrubs.
Papa Acachalla is his fraternal (i.e. not identical) twin brother who looks nothing like him. Their relationship hasn't been explained much other than a few short lines of exchanged dialogue. But it seems like Acachalla has helped Nadachalla in the past and Nadachalla comes to Acachalla in times of distress when he needs great help.
Having met Gertrude for only a few moments, the first impression wasn't well as Gertrude was furious by Nadachalla's flirting with a princess. Gertrude then chased Nadachalla for an unknown length of time.