I (27F) want to start by saying I have NO moral issues with doing this. My brother (26 M) is trans and I have never outed him and have/will always keep things private if he wants me to. I would gladly do this for his girlfriend (27F) too - morally speaking.
The issue I have is a bit delicate, so please try to approach with sensitivity.
My brother is someone who could fully pass for a cisgender man. His girlfriend is extremely beautiful, feminine, and rarely gets misgendered. That said, when most people meet her for the first time, they can tell she is trans. I won't go into details as to why, out of respect for her, but please trust me that people can tell.
Her and my brother have asked me not to mention she is trans to my parents and I agreed - but I thought it was more the case that he wanted to be the one to say. A
fter meeting her, my parents could see she was trans and mentioned it and he completely denied it. The same thing happened with another relative.
As far as I know, he plans to not tell anyone in the extended family, and wants me and the only other person who "knows" to keep it a secret.
He is fully under the impression that people believe him. If anyone suspects she is trans, he writes them off as only thinking this because he is trans and so they are making false assumptions (not because of what she looks like).
She met some of my friends at a party recently -
people didn't misgender her, but afterwards would mention she was trans as it it was matter if fact/widely known. Ie they weren't asking "is she trans?", they were taking it for granted that she was AND that she knew they knew. Even people that didn't know my brother is trans did this. She and my brother do not know this because, by coincidence, it happened when they weren't there (it's not as if it's a constant topic of conversation).
Next year I am getting married. This will be her first time meeting large parts of my extended family. I feel I am in a lose lose situation.-
if I let her go into this, not knowing people can tell, then if anyone (of 100 guests) mention it, it's a shock on a day where they are both under pressure and the assumption from their perspectives will be that I betrayed their trust and told people. - if I speak to my brother and tell him, I challenge their view of her as being stealth. Maybe this is important to her identity and it damages her confidence.
All things considered,
I am thinking it's best to gently tell my brother that multiple people have been able to tell, and they will attend the wedding, but maybe I don't mention the full extent / how many people have been able to. So at least then they are prepared for a worst case situation.
Can anyone offer thoughts or advice?