I just did the same thing today with my mother, and I feel great, like the weight on my shoulders has been lifted, and the storm clouds are lifting. I don't think my sister needs to find out at this time, at least not until it becomes noticeable.
It's interesting how so many things in life aren't as scary as I make them out to be. In the last two months I've already proven that to myself three times. It's not my last talk with my mother, she does want to know more now. Sounds like I may be able to count on her for supporting my transition after all, which is a great relief to me.
~Marciel