Final answer:
The Vicarious' plan is kept secret, and the number of people they tell is not specified. Santiago is not informed likely because he quit the academy and left for Puerto Rico, separating him from the group's confidential matters.
Step-by-step explanation:
The Vicarious do not explicitly mention how many people are told about their plan. However, the text suggests that the information is kept within a limited circle, as there is a tone of secrecy and concern about the implications if their plans were revealed. This need for confidentiality likely explains why Santiago is not informed. Santiago has removed himself from the situation by quitting the academy and moving back to Puerto Rico, implying that he is no longer part of the inner circle and, therefore, not privy to such sensitive information.