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.
Maha Zoldyck, was stated to be the father of Zeno Zoldyck but this was retconned later on. Maha Zoldyck is stated to be the grandfather of Zeno.
Maha Zoldyck is the only known
Enhancer in the Zoldyck family. He was the one-sided rival of Isaac Netero and the only one known to survive a bout with him. Isaac Netero even once said that Maha was once the strongest fighter during his prime.
There's still no confirmation on who Maha's son is but we can assume that he is the very first Transmuter in the Zoldyck lineage, likely as a result of Maha's wife. And likewise, no confirmation about the grandmother.
Zeno is the father of Silva Zoldyck. (see their similar nen-type.) Killua's mother calls him father because Zeno is her father-in-law.
Maha was about 120+, and Netero was about 110+. Zzigg Zoldyck was a kid at the time of Netero’s expedition of the dark continent, and Netero was most likely old enough to have children. This means Maha most likely was too (being roughly around the same age as Netero), so I’d say it’s Zzigg Zoldyck that is Zeno’s father.