This is another good clearinghouse of info:
https://www.glaad.org/transgender/allies.
My daughter's BFF is trans (16yo). We have another friend-couple that has a trans child (18yo now).
It has been incredibly mind-opening and rewarding to get to know not just the kids but the parents too.
I would recommend you "go slow" and give the family every courtesy and benefit of the doubt as they navigate this. I can truly say that as an outsider you have no idea of what it's like to be trans or to be the parent of a trans child. Educating yourself takes the benign ignorance level down a lot but only spending time with the family over the long span will really create full understanding. If it's meant to be...maybe you won't be able to wrap your own head around it.