Brian’s jealousy and Peter’s desperation show a deep-seated human (and canine) need to be the "favorite," suggesting that our self-worth is often dangerously tied to how much attention we receive from others.
The cat’s ability to turn the family against Peter serves as a dark comedy take on how easily people can be swayed by a polished exterior, ignoring the loyalty of those who have been there all along. Family CatFamily Guy : Season 19 Episode 19
This specific episode, "Family Cat" (Season 19, Episode 19), is a sharp look at how a new presence can disrupt the established of a home. "Family Cat" (Season 19