Trans relative

I hope I get some support or someone in same position as I'm. My sibling is trans, he was born girl and now about half year ago he told that he is trans guy. I'm okay with thought and support him, but I feel bit confused. If I meet new people, I tell them that I have brother, but my old friends think that I have sister. So, if you have trans relative or close friend, like sibling, cousin, parent, child or partner, I would like to hear your thoughts. And sorry if my terms are wrong, I'm not familiar with that subject.