"할아버지께서 차에서 주무십니다."
Translation:Grandfather sleeps in the car.
Yes, his age and status as a father and grandfather require the use of honorifics who is not in his age cohort, regardless of perceptions about his economic situation. Not using honorifics to speak about him would be rude. Not using honorifics to talk to him would also be rude unless he permitted the familiar address. Even then, I'm not sure a younger person would be comfortable with dropping the honorifics.