Going up to my parents soon to celebrate their 50th anniversary and my 2 (straight) sisters are going to be there that weekend. No spouses there just us three and my one sisters son, and maybe my daughter (whom I am already out to). My sisters I a certain remember what a strange boy I was, as I am the middle child. Plus my older sisters eldest child is also a transwoman, about 2 years into HRT. If they accept me, which I think they will /crossfingers I will get their opinion if I should come out to me elderly parents... Any advice?
Well if they accepted their own daughter chances are they'll accept you no matter what. Sisters are their to spread love love. When did I get so soppy sounding?
I'd say, talk to your oldest sister, and possibly your niece. They will likely have the best knowledge of how your parents will take it.
Take it slow. Casually ask them what they think of gay marriage, LGBT rights, etc. Then, come out to the people you think will react the best one at a time.