Is expiation for an oath obligatory after two consecutive oaths to do something, then going back on it, or is it not obligatory? And if it is obligatory, is it for one oath or for two?

If you swore twice and broke your oath, the ruling depends on your intention. If by the first oath you intended never to take the juice, even for a price, then this is an independent oath from the second, and two expiations are incumbent upon you. However, if by the first oath you intended not to take the juice for free, then the second oath is considered a confirmation of the first, and only one expiation is incumbent upon you; because repeating an oath concerning the same thing necessitates only one expiation. It is stated in "Kashshaf al-Qina'": "And whoever repeats an oath, the requirement of which is one, concerning a single action... then there is one expiation; because its cause is one, and it is apparent that he intended confirmation."