ANSWER
A. Their
EXPLANATION: The club is owned/belongs to Haitian
Being mean to another person based on the fact that they angered you in some way is easier to do, but on the contrary understanding that what the person did to you is more difficult.
Answer: It could be A or B
Explanation: I´m having a little inner issue with the fact tha there are 2 parts of the volcano that match your question.
Crater: It could be considered as the central vent of the volcano. Some of these might be even as bigger as the whole stucture of the volcano.
Boiler: This could be define as a depression inside the crater, it could be very very deep, almost at the size of the whole volcano.
Swift is making a satirical statement of several concepts.
One would be on the objectifying of humans (computed cost for babies...)
Two would be the idea of how they can easily spare the children by merely reducing them to costs, especially from poor parents.