If I recall correctly, the grandfather of the current Zengoro was adopted. So since then, it's pretty much straight. He showed me the pictures of his family. To his grandmother, who was "originally" Houshi, if you will, but not his biological grandmother, he refers to as "my grandma".

Houshi have a different understanding of family than we do. For them, "family" and "business" are the same thing. For example, the daughter never calls her parents by mom and dad while in the hotel, but by their titles (Okami and President)

[edit: got a bit confused who did what with grandma]