Final answer:
Brutus is inclined to join the conspiracy to maintain the Roman Republic and prevent the establishment of a monarchy, thus continuing his family's legacy.
Step-by-step explanation:
Brutus is inclined to join the conspiracy for the reason outlined in option B) To maintain the republic and prevent a monarchy. The line "My ancestors did from the streets of Rome/The Tarquin drive when he was called a king" (lines 53-55) refers to Brutus's ancestors who were instrumental in overthrowing the Etruscan kings and establishing the Roman Republic.
This historical context implies that Brutus feels compelled to protect the Republican form of government against the threat of it transforming into a monarchy under Caesar's rule, which is considered tyrannical by some members of the Senate, and to uphold his family's legacy of defending the Republic.