Evelyn,
Surprising people can be a really mixed bag. The reaction may be more negative than had you prepared them for the change in some manner. You are talking family here, and if you are close at all they deserve a bit of consideration. Yes, this may take a bit of undercover work to see how they might react. I have been doing a bit of that with my daughters, and thought I was being really stealth. Yesterday an email from my oldest asked point blank "Has Erin taken over and you are afraid to tell us?" That still doesn't tell me how they would react, but I am pretty sure I can work with it. If I were to show up out of the blue with a blonde wig, makeup, feminine top, denim skirt, and feminine sandals it might be too much (I sort of shocked my therapist that way...)
You need to do what suits you and your best read of your family.
HTH
Erin