Idk maybe tell them they should join a trans parent group on facebook or something where parents help teach each other. It shouldn’t really be your burden to educate them solely. And in some ways you can’t educate them. As for how to get more comfortable talking to them i would say build a good foundation of trust and love
Like talk about how it can be difficult for any child to talk to their parents about topics like this and it’s not a reflection on them as parents but a reflection of possibly fear of societal rejection. You need to feel safe opening up and they need to be allowed the grace to be human and learn