Why does the entire family engage in this?
Radak: It is for the reward that they will get for it.
Malbim: It is so all will have a share in it - "in order to anger Me."
What are "Kavanim"?
Rashi: It is a mold in the form of a star.
Radak: It is kinds of food that they served to Meleches Shamayim. This is like "Asinu Lah Kavanim" (44:19), "v'Es Kivun Tzalmeichem" (Amos 5:26). Perhaps it is called Kavanim, because they directed their hearts and minds to them, to make them nicely.
Radak citing Targum Yonasan: They are robes.
What is "Meleches Shamayim"?
Rashi, Targum Yonasan: They gave this name to a great star. It is an expression of Malkah (queen).
Radak: This is like Meleches Shamayim with an Aleph (the result of the creation of Shamayim, i.e. the stars), just the Aleph is omitted.