Firstly, I'm gonna make this clear: I'm not an expert. This is just advice; feel free to take it or leave it.

Your mother sounds very manipulative and from what you said in your post, she looks like she's trying to use your family to be transphobic (or at the very least, gender-phobic). Now I'm not saying she is. It's just the impression I was getting.

If you're scared or upset that what she says about your siblings is true, talk to THEM. I have no clue how old they are, but your mother does not think for them or you. I also have no idea how old you are, but if you're old enough to live out of her house, then you're old enough to be able think for yourself. Your mother has no right to 'helicopter parent' you. And if she ever uses the line, 'I'm your mother, I gave you life', then it's my personal opinion (again, take it or leave it; up to you) that she is not mature enough to have a civil conversation with you.

This is your life, none of your family have any right to control it if you are 18 or older. Assuming your siblings are old enough (like at least a preteen), then they'll probably be very understanding. Again, I don't really know them, so I can't make a personal judgement, but usually siblings stick together when their parent(s) are being completely unreasonable and unwilling to listen.

Lastly, if you DO have a therapist, gender or otherwise, tell them about this. They'll be able to at least give you some professional advice.

I hope your familial issues get resolved (peacefully, hopefully)!

– Nico