Hey Josh,
That's a good idea to wait and make sure it's what you want.
I would think if you know that your father and sister love you unconditionally then it might be easier for you to tell them when your ready too.
When I told my mom, I thought she would cry, but she didn't. Maybe that was b/c I was so upset and crying. She said she'll always love me no matter what. I thought it would be a long time before I told my mom, but the way I told my mom was... well, it came out in a fight. After the fight was over and we started talking and I was crying, I told her there was something I've been wanting to tell you for a long and the words wouldn't come out... and she asked if I was gay and I told her no, then she said... you wanna be a boy... and I said yes. So she knew, but like me she kept herself in denial even though all the signs were right there. And when I told my grandmother, I had my cousins with me.
So when your ready to tell your Father and sister it might be easier to have someone with you. It was a lot easier for me telling my grandmother with my cousins right there with me and helping me talk and backing me up.
I feared that too, but in the back of my mind I knew that my mom loved my unconditionally. It's always scary to tell family a secret you have and afraid they will stop loving you b/c of it.