How Did Eisav Sell the Birthright?
The Birkat Avraham comes along with the command not to take a wife from the descendants of Canaan. Therefore right after Yaakov receives the bracha he marries into Yishmael's family.
How was Yaakov able to buy the birthright - a kinyan can't be made on a דבר שלא בא לעולם? Why does the pasuk refer to Rivkah as the mother of Yaakov and Esav?