They were born into them.
Yes, they know this from the very start of the play.
Romeo kills Tybalt. As a result, he incurs such hatred from Juliet's mother that it becomes impossible to announce Romeo and Juliet's marriage to their parents. If the parents don't know that Juliet is married already, they will arrange for other marriages for her, like one to Paris.
the balance of power is romeo and juliet loved is other however they know that their families are enemy and they won't accept on the other hand they love their families aswell.
He helped Romeo and Juliet by "marrying" them. He also helped by giving the potion to Juliet to put her into a death-like sleep. Unfortunately, both of these ways that Friar "helped" ended up backfiring, mainly giving Juliet the potion, because Romeo didn't know she was only sleeping and ended up killing himself.
Romeo and Juliet's families hated each other. Romeo did not want her to know that he was a member of her family's hated family.
Nurse helped Romeo and Juliet because she loves Juliet. Juliet didn't want to marry Paris and Nurse stood by her (at first). Nurse was the one who raised Juliet and she cares about her. Juliet is hurt when Nurse betrays her by advising her to marry Paris after Romeo was banished.
Conflict is shown in Romeo and Juliet when Romeo and Juliet fall in love even though their families hate each other. It creates a problem because they know that their families won't be able to accept them because of the hating thing. I'm 14 years old and never learned anything about Romeo and Juliet . anyway, hope I helped!
Friar Laurence hopes that if he marries Romeo and Juliet that the feud with their families with end. Little did he know that will not happen until they are no longer living.
The Montagues and the Capulets both pronounced as in English, not French. Why not more traditional names like Capone or Mastrangelo? they are two rival gangs in the Old Country, you know the Mafia.
at first she doesn't, but he tells her he is there eventually
I don't know who put Romeo & Juliet, but I can assure you it was wrong. Romeo & Juliet were a tragedy, written by Shakespeare, about 2 children madly infatuated with each other, much like teenagers today. Also this question is based on opinion. So that depends on how you feel.
Their families, I guess. They already know about it before the play starts, since they know about it in Act 1 Scene 5 and we don't see anyone telling them.