Well, Mercutio was invited. But as for Romeo and the rest, Capulet didn't mind as long as they behaved themselves.
Romeo and his friends plan to hide their identity at the Capulet's party by wearing masks. This allows them to mingle with the guests without being recognized.
In Act I Scene 5 Tybalt tells Capulet that Romeo, a Montague, has crashed the party. Capulet tells Tybalt not to bother about it: Romeo has a good reputation, and is behaving himself, so why disturb the party at which everyone is having a great time?
Romeo's friends, Mercutio and Benvolio, convince him to go to the Capulet's party to meet new young ladies. They encourage him to forget about his unrequited love for Rosaline and to have a good time at the party.
at the Capulet house in the yard... i think.
Romeo and his friends learn about the party at the Capulet's through a servant's invitation list that is accidentally shown to them on the streets of Verona. They decide to attend the party as an opportunity for Romeo to see his love interest, Juliet.
Benvolio tells Romeo that Juliet is a Capulet at the party.
Tybalt becomes upset when he recognizes Romeo at the Capulet party, as he sees it as a direct challenge to his family's honor. Capulet responds by scolding Tybalt for causing a scene and tells him to calm down and let Romeo enjoy the party, not wanting any disruption to the event.
Tybalt leaves the Capulet's party because Romeo and his friends have shown up, and he is angry that the Capulet's will not make him leave. Tybalt wants to fight Romeo right there, but Lord Capulet stops him and angrily orders him not to ruin the party.
He can't read it, being illiterate.
challenge him to a duel for attending the Capulet party without an invite.
Capulet tries to diffuse the situation by telling Tybalt to calm down and not cause trouble. He also reminds Tybalt that Romeo has a good reputation for behaving peacefully and is not worth fighting with.
He gets all fired up. He wants to go confront Romeo and fight him for coming to a Capulet party, but Lord Capulet tells him to shut up and be nice. He doesn't want the Prince coming and ending people for starting a fight.