A marxist class analysis clears this issue up pretty well, as its based on the relationship to labor and capital. The example interviewee would be working class based on their relationship to capital. Grandparents that own a hotel (assuming its not a large chain) would be petite bourgeoisie, as they own a small amount of capital, but must work to make it productive and are therefore still a kind of working class. The accountant father is still working class, as he must work for a living, but would be considered Private Managerial Class, as they are rewarded well for their skills within capital.
