I can relate to your friends. When Hypatia came out to me, I didn't know anything about transgender people except what I had seen in the media, which mostly seems to sensationalize it. I knew I accepted her, but it was still an adjustment and a learning curve for me. She filled me in on a lot of information, especially about her own story, and gave me links to other places for more general info.
At first, I was afraid of accidentally saying or asking something wrong and having it sound offensive. I would say to make sure your friends know that you'll understand if they ask something that could be taken the wrong way. If they're asking respectfully because there's something they want to understand, they need to know you won't get upset if they mess up.
It sounds like the friends you've come out to know each other. When Hypatia came out to me, I had to keep it a secret for months. This made it harder for me to process. I think your friends can be a great support to each other, which will make them able to be a better support to you.