What is the body count at the end of the play?Who dies, how do they die, and in what order do they die?

Each of the above is true, bringing your death toll to 5.
However, there are some additional details worth
noting.

Mercutio, the first death, occurs because Tybalt
wants to fight Romeo and Romeo won't fight. He starts talking about how he loves Tybalt
and Tybalt has no comprehension of why Romeo is talking like this, which makes sense
because Romeo and Juliet are keeping their marriage a secret. Mercutio can't stand to
see Romeo be such a push-over and tries to instigate a fight with Tybalt. Romeo tries to
break it up and Mercutio is hurt "under [Romeo's]
arm."

Romeo kills himself because he
thinks Juliet is dead. She really is getting ready to wake
up.

Juliet kills herself because she knows
Romeo is dead.

When Lady Montague hears of all
of this, she cannot bear to take any more of the feud between the families and her only
son's death scarred her more than she imagined. Thus, she seems to have chosen to take
her own life.