In the final scene, the Prince speaks rightly when he blames Lords Capulet and Montague for not only Romeo's and Juliet's deaths, but also for the deaths of the Prince's own relatives. The Prince blames their hatred and their feud for all of these deaths. We see this accusation in the Prince's lines:
Where be these enemies? Capulet, Montage,
See what a scourge is laid upon your hate,
That heaven finds means to kill your joys with love!
And I, for winking at you, discords too,
Have lost a brace of kinsmen. All are punish'd. (Act 5, Scene 3)
However, others are also indirectly responsible for Romeo's and Juliet's deaths. While Friar Laurence broke no law nor holy sanction in marrying Romeo and Juliet without parental consent, even though his motive seems noble, one has to question the sensibleness of his decision. Friar Laurence agrees to marry them because he believed the "alliance may so happy prove, / To turn your households' rancour to pure love." In other words, he believed that uniting Romeo and Juliet in wedlock would put an end to the feud. The flaw in his plan is that the marriage was performed in secret with no immediate plan unveil the marriage. Had he been wiser, he would have foreseen that the ongoing feud would prevent any real relationship between Romeo and Juliet, sabotaging his efforts to create peace. Instead, he should have postponed the marriage until he, himself, could prepare Lords Capulet and Montague for the union. Friar Laurence continued to make things even worse by lying to Lord Capulet in helping Juliet fake her death. For all of these reasons Friar Laurence is indirectly responsible for their deaths. However, he is rightly pardoned by the Prince, because ultimately, their deaths are the fault of Lords Capulet and Montague.
Tybalt is also indirectly responsible. Had he not had such a hot-headed temper and instead agreed with his uncle to let Romeo alone for crashing the ball, Tybalt, as well as Rome and Juliet, would have remained alive. Tybalt's death led to Romeo's banishment, which led to both his and Juliet's deaths.
Finally the Prince also holds himself indirectly responsible because he did not check Lords Capulet and Montague sooner, nor try to stop the feud sooner. His personal blame is seen in the line, "and I, for winking at you, discords too, / Have lost a brace of kinsmen."