In the Zoldyck family is something known about the grandmother and the grandgrandfather? it is known that there are 10 members in the Zoldyck family. But do you know something about the grandgrandfather and the grandmother? Zeno Zoldyck is the grandfather. But father of who he is? From the father or mother of Killua. I think it's from Silva Zoldyck (the father) But in the episode Gon, Kurapika and Leorio go to find Killua, Killua's mother calls him father. Then how to know who the father really is?
Zeno Zoldyck is the father of the Silva Zoldyck. It is clearly stated in this family chart which in the HxH wiki. In the family tree, Maha Zoldyck is the grandfather of Zeno, also he is the oldest living person in Zoldyck Family. 



There are no mentions about Zenos' wife (mother of Silva). Below image shows the family of Zoldyck but Zenos' wifes' image is missing there also. Also, Kikyo is the only women that have mention and appeared in the HxH from Zoldyck family (apart from Silvas children). I think that mainly because of they joining Zoldyck family from the other families.