Who are the individuals involved in the "almost" fight?

When the Montague servants – Abram and Balthasar – arrive, Sampson bites his thumb at them (which is rude but not illegal). Insulted, Abram confronts Sampson and a fight begins.

Benvolio, Romeo's cousin, arrives to discover the fight in progress. Drawing his sword, he commands them to stop. Then, Tybalt, Juliet's cousin, walks onto the street. Upon seeing his rival, Benvolio, Tybalt also draws his sword, reigniting the altercation.