I was downstairs with my oldest brother when he asked the question, "Are you actually happy with being a girl, or do you wish you were a boy?"
Alarmed by the question, I replied, "I don't really care." far too quickly for my liking, and the conversation dropped there. I was kind of shaken afterwards, though. I'm supposed to keep quiet for a while. I mean, he's already catching on and I really don't want him to, in fear of my own safety. I feel lucky for what I did end up saying, however. I could've easily said the truth without thinking.
Any advice for when things like this happen in the future- how to deal with questions like these?
If you're considering coming up with a response to have at hand in these situations, it helps to put it in the context of what you wish to seem to think of the question, rather than answer it directly and lie. Pretend you've just been asked something incredibly weird, like "What would you do if you had another nose on your face?"
The response would not be to answer, but more to look confused and say something like "What kind of drugs are you on, and where do I get some?"
This also buys you time while you gauge the situation ;)
Only you can know the details of your relationship with your brother, and determine whether this would be a positive or a negative thing. He's definitely going to know the truth about your gender & sexuality eventually - your whole family will - so that Band-Aid is going to have to be ripped off at some point. Is this the right time? Is he the right person to confide in? Only you can decide.
But one thing is obvious: your brother knows something already. He has either picked up on your distress, or your mother has mentioned something to him in passing and he's now trying to figure out whether she was telling the truth.
Why do you think he's doing this? Would he do this to find a reason to attack you, or is he generally supportive? Is he offering you a shoulder to cry on? Could he be an ally to you? Could he provide a safe haven within your otherwise unsupportive family? Would he offer to be your 'mentor', guiding you in learning the male socialisation he took for granted?
He's just given you a window of opportunity: you've been struggling with your internal demons for years, and he's offered you a chance to talk about them. If you think he might be supportive, it might be a good idea to have a chat with him. You can keep it generic, something like "You know what you said about me being happy being a girl? Well, to be honest I've been struggling with that question and I do have some doubts". Use that sort of thing as an opener to a conversation, and see how he responds before you divulge any sensitive details.
However, if he's the abusive type who might be trying to get info out of you so the family can use it as more ammo with which to hurt you, keep your head down and deflect these questions if you think that's the safer option.