You have a couple different questions, but the main one seems to be in regard to Abraham and Jesus.
Abraham and Jesus
Abraham is only the ancestor of Jesus in His incarnation. Orthodox, Catholic and Protestant branches of Christianity teach that God is and has always been a Trinity of Father, Son and Spirit. The Son became a man and entered into His creation around 2000 years ago. When He did so, He was given the name "Jesus", which means "God saves". He was named this because He came to save.
However, Jesus, or God the Son, existed "before Abraham". In fact, it was likely God the Son in a pre-incarnate appearance Who visited Abraham prior to the destruction of Sodom. He was also likely the fourth Man in the fire with Shadrach, Meshach and Abednego, whom Nebuchadnezzar described as one "like a son of God (the gods)".
Even in creation, God says, "Let us make man in our image, in our likeness..."
So, Abraham did worship God the Son before He became a Man and took on the name of Jesus.
Briefly, the Trinity is something that is seen in much of creation. The physical universe consists of 1) time, 2) space and 3) matter. The three are co-existent. Time itself is measured as 1) past, 2) present and 3) future--it is one, yet a distinct three as well. Space is measured in 1) length, 2) width and 3) height--three distinct dimensions. Matter exists as 1) solid, 2) liquid and 3) gas, as H2O can be ice, liquid and vapor, yet still the same substance at its atomic level.
So, the concept of a three-in-one unity is not without example in creation itself. These examples are understood to be reflections of the Creator.
God never divided from One into Three. He has always been and will always be Father, Son and Spirit.