The Biblical Geneologies is not as we understand geneologies. In the Hebrew geneologies, there is no grandfathers, great grandfathers, etc. Their usage of the words 'mother' and 'father' is not the as we use these words today.
In Hebrew, A Father is the father of his son and daughters, and he is also father of his Sons and daughters children, and he is the father of what we call great grandchildren, and so on.
Same is true for mothers. A mother of her children is also called a mother of her grandchildren, and also mother of her great grandchildren, and on and on it goes.
So we use modern English, Spanish, French, etc. reading someone begat someone in the OT, and we assume that begat means a parent to child direct relationship. But to God's people of the Exodus and through the later Israelites, 'begat' merely means ancestor of - whomever's name comes next in the lineage. In fact, in Jesus day, all Jews simply referred to Abraham as "Father Abraham". Abraham is their father because they were simply descendants of his seed.
I highly recommend Walter C. Kaiser's books: 'Hard Sayings of the Hold Testament', and his follow up: 'More Hard Sayings of the Old Testament.' Walter Kaiser is a trusted OT Scholar and well respected expert on the OT.
In the book "More Hard Sayings of the OT" Prof. Kaiser addresses Hebrew geneology in his chapter on "Exodus 6:16-20, and Exodus 12:40 - Three Generations of Levites During 430 Years in Egypt. LOL :)