How was Isaac and Jacob blessed?
In the times of the Old Testament children could inherit two things from their parents: property and a blessing. If your parents had three children, then on their death their property was divided four ways (one more than the number of living children). The eldest child generally received two portions and the remaining children received one portion each. Along with the double portion, the eldest child generally received a blessing from his father. The blessing was a prophecy about his future and the future of his descendants. When a child received the blessing, he was then made the head of the family after his father's death.
Most of the time the double portion went to the eldest child, but sometimes the father might choose to give it to another child. The blessing also might not be given to the eldest child because the child displeased his father in some way.
Abraham was given a special blessing from God (see Genesis 12:1-3; 17:1-14). As long as Abraham's descendants remained faithful to God, they were allowed to pass that blessing on to their children. One blessing is that Abraham's descendants would become a mighty people. Another was an inheritance of the land of Canaan. But the most important blessing was a promise of a person through whom all the nations of the world would be blessed (in other words, Jesus Christ).
Abraham passed the blessing on to Isaac as God had told Abraham (Genesis 17:15-17). The actual giving of the blessing (and the inheritance) was recorded in Genesis 25:5. God told Isaac and Rebekah to pass the blessing to their second born son, Jacob (Genesis 25:22-23). The blessing is implied in the phrase "the older shall serve the younger." However, when Isaac's two boys grew up, Isaac liked the older boy better because of the meat he brought home (Genesis 27:1-4). Isaac decided to give pass the special blessing to Esau instead of Jacob. Rebekah happened to overhear Isaac's plan and she helped Jacob trick Isaac so that he blessed Jacob instead of Esau (Genesis 27:18-29). Jacob blessed each of his own children, but he passed the special blessing to his son Judah (Genesis 49:8-12). The special blessing is always seen in who is declared the head of the family.