Only one blessing? – Tol’dot
True, Esau was not a very nice character, but he was Isaac’s son after all and surely justice and logic should dictate that there should be a blessing reserved for him.
Rashi says that Esau had a conscience after all and deep down he realised that Jacob despite his defects – was really more entitled than he was to their father’s blessing.
Isaac was on the other hand a rather weak person, wracked with uncertainty as to whether he might have done the wrong thing in giving Jacob the blessing.