Dark brotherhood

[Guest Nic]

I made a big mistake I killed one of the three hostages planning to join but accidentally used fire breath on astrid and she starts attacking so I ran out and saved the game she did not die and destroying the brother hood quest did not start it still says talk to astrid but when I go to the clan every one tries to kill me but I can't kill them

[David]

I'm assuming you're talking about the "With Friends Like These..." quest since there are three hostages. The reason the DB is attacking you is because you never finished that quest, which is necessary to join their faction. You'll have to go back from where you ran away from Astrid and talk to her. If she tries to attack you, try holding down the "sheath weapon" button.