Having already related the dream to his brothers, why does the Torah repeat "to his brothers" again?
Rashi: Because, after telling his brothers about it, he related it to his father in front of them. Ha'Emek Davar - he did not ask them, for they would not want to hear it, They did not interpret it, so that it would not be fulfilled, so he told it again, also in front of his father, who interpreted it. 1
Why did Yosef not also relate the first dream to his father?
Ramban: Because he himself understood the obvious interpretation of the dream.
Sifsei Chachamim (citing the Maharshal): Because his brothers had already interpreted it for the good. 1
Hadar Zekenim: Yosef understood that only this dream applied to his father.
And he knew that a dream takes effect according to its interpretation.
Why did Yakov dismiss the (second) dream out of hand?
Ohr ha'Chayim: Bnei Yakov would not get greatness via the other nations, only via their father - if so, it is not feasible that Yakov would bow to him. He said so to dispel the brothers' envy.
Rashi #2 and Ramban #1: He knew every dream contains some nonsense. 1 He dismissed it due to the fact that Rachel was no longer alive 2 , only in order to prevent the brothers from becoming jealous. 3
Ramban #2 and Seforno: He thought that the dream was a sign of Yosef's haughty intentions to rule over his family, and he was merely 'carrying his thoughts on to his bed'. 6
Malbim: Yakov wanted to interpret his dream favorably, but also avoid envy of the brothers.
Which the Gemara in Berachos 55a, learns from here.
Rashi: He did not know that the moon referred to Bilhah, who raised Yosef as a step-mother.
Moshav Zekenim: Since a dream is fulfilled according to its interpretation, why is this incredulous? First Yosef told Yakov, and Yakov interpreted it, and then he said so to the brothers to prevent envy.
Malbim: A father does not bow to his son. Also your brothers, who are more numerous and mightier than you, will they bow to you?!
Who were the sun and moon who were destined to bow down to Yosef?
Rashi: The sun represented, Yakov. The moon really referred to Bilhah, 1 who raised him after Rachel died (but Yakov did not realize this).
Ramban: The sun represented, Yakov. The moon represented all the seventy members of his household. (There were also eleven stars, for Yosef's eleven brothers, bowed down to him before Yakov and the rest of the family arrived.)
Da'as Zekenim (9): When Yehoshua told the sun to stand still, it did not want to. He told it, you already bowed to my ancestor!
The Ramban however, maintains that Bilhah and Zilpah died before Yakov and his family went down to Egypt, in which case the moon could not have referred to her either.
What is the exact meaning of 'Hishtachava'ah'?