You will be fine.
Seek out support, either via disclosure among your sister or joining a group. Having the support of a group made my diagnosis and subsequent mastectomy bearable. I felt like I had a lot of good information as a result as well. It felt good to have so many people on my side. I was in shock and not thinking clearly at the beginning. So much information to digest.

I just went through this last year. Please PM if I can help. I am super fine now.