Could Jacob actually be considered more of the father of the nation of Israel than his grandfather Abraham being that he had 12 sons for the 12 tribes?
Jacob is most directly the father of Israel because his sons are the fathers of the twelve tribes of Israel. However, many miraculous events happened from the time of Abraham to the time of Jacob. Without Abraham, there is no Jacob or twelve sons of Israel.
Abraham left everything he knew to go to the land that would become known as the land of Israel. And when he was traveling there, God established his covenant and promise with Abraham first.
Without Abraham, you don’t have the promised and miraculous son Isaac, Jacob’s father. Without Isaac, there is no Jacob. It was with Abraham that God made the promise of a great nation, Israel. And Abraham is the first to receive and enact the sign of that covenant, circumcision, which becomes one of the marks of the nation of Israel.
The foundation of Abraham was absolutely necessary for anything else to happen that gave God the nation on earth that he would call his own. You also need Isaac before you can have Jacob for the same reason. God reasserts his covenant with Isaac.
Rebecca is also barren like Sarah for a time until Isaac prays for her. It is from Isaac and Becca that Jacob and Esau are born. You cannot have one without the other. Because God establishes his covenant and promise with Abraham, and then continues through Isaac, you need Abraham.
Abraham is not only the grandfather of Israel, but he is also the father of faith, as the New Testament tells us. He is the one who lays the foundation not only physically but also spiritually for the nation of Israel.
God is pleased with Abraham, and so his family line continues with the promise. At no place in the biblical account is Abraham not credited as the father of Israel physically and spiritually.