The Gymnast - S6-E6
Continuity mistake: When George is at his girlfriend's mother's house, the plates on the table switch around. Then the order he stacks them changes. When he picks them up, the plate with the chicken is in the middle with a plate with a napkin on top, then in the kitchen, the plate with the chicken is on top.
Chosen answer: George does mention his brother in the episode "The Parking Space". They actually really never mention anything that contradicts the fact he had a brother though, it just isn't mentioned.