I'm transgender and I don't know how to tell my family
Why do you feel scared about this?
I'm afraid they will disown me
It is okay to be transgender, as this is the way that you were born.  Your family should support you in life, but it's okay to be unsure about how to bring this up to them if you are afraid of their reactions.  It might be best to test their reactions by mentioning  a "friend" that you care about deeply.
Thanks. I think I'm going to tell them this weekend.
Well after you do that I think you should talk with a therapist. Things might not go the way you thought they would and having a back up can provide extra security.