Freedom of Choice vs Sold Game

If Esav leaned toward idol worship before he was even born, where was his freedom of choice? Rashi says the twins were already pushing in Rivka's womb, one toward the doors of Torah and one toward avodah zarah. The Rambam seems to say both things: in Hilchos Deos that traits are inborn, and in Hilchos Teshuva that every person chooses who to be. How can both be true, and what was Yitzchak thinking when he prepared to bless Esav? Your own natural temperament looks different once the two are put side by side.