Continuity mistake: When they initially pull into the handicapped parking space, George is driving a large yellow Cadillac. When they return to see the car destroyed, it is now a much smaller blue car.
Continuity mistake: When Kramer enters Jerry's apartment, he closes the door. In the next shot, the door is wide open. A few shots later, George opens the door, which was closed when he entered.
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.