Like many of us, Rebekah started out being spiritual. She accepted the God of Israel and she sought God during the pregnancy. However, at the time of the deception involving Isaac and Jacob, she did not place her trust in God to fulfill His promise of "the younger ruling over the older" wherein Jacob would rule over Esau.
I believe Isaac was more spiritual than Rebekah, but they seemed to not be communicating with God during this time of their life. Without communication between husband and wife and God, Rebekah and Isaac took things into their own hands when it came to giving the blessing of the birthright. If they had sought God, He would have instructed them on the birthright.
Jacob had greater spritual understanding than Esau because Jacob understood the significance of the birthright and he probably had been told by Rebekah about the promise God had made to her. Esau scorned spiritual things and was only concerned about being cheated out of his birthright. He didn't care that the birthright was a privilege from God.