How to deal with family

Hello everyone!

I wanted to ask the best way to support my trans female cousin who is visiting soon. I am a trans masc nonbinary person, and I am somewhat out to my immediate family, but not to my extended.

My cousin is out to our whole family, and she lives in a different country, but is moving back and will be visiting us.

What is the best way to go about supporting her? I know I will use her correct pronouns, her correct name. But how do I make sure our relatives do to, whether or not she is there?

I also wanted to ask if my coming out would make things better or worse for her? I wondered if I come out, that might take heat off of her. But coming out as nonbinary is really scary, and mentioning the trans masc part is really really scary.

Thanks for any advice you might have