First Tybalt is one of the people who are responsible for the tragedy. Tybalt hated the Montagues already, and when Romeo showed up to the Capulet party, Tybalt overreacted and got angry at Romeo and that made him angry and resulted in killing Mercutio (I, i, 55-96). Lord Capulet said, don’t do anything to Romeo, but Tybalt didn’t listen because he was too angry for Romeo even being at the Capulet party. Also If he had just little kindness in his heart, Mercutio and Tybalt would’ve lived and Romeo wouldn’t be banished (III, i, 112-128). This resulted it in Romeo’s banishment, and in the end, his death, along with Juliet. Romeo’s banishment led to Friar Lawrence’s plan and Friar Lawrence is also responsible for their death from his own Plan
Finally Friar Lawrence is responsible for the tragedy because he came up with the whole death potion plan to Juliet, but it failed and killed Both Romeo and Juliet (IV, i, 70-78 and whole of Act V). Friar Lawrence has to take a big responsibility for this tragedy, because the plan didn’t go as though he did. Addition to that, if he sent the letter faster, Romeo would’ve carried out the instruction and Romeo and Juliet wouldn’t be dead (V, ii, 5-12).
The letter had instruction for Romeo to do, but Romeo couldn’t get it because Friar John was forbidden