Hey Leah!
Do you know Jazz Jenning's book I AM JAZZ?

It is a (real) story about a trans girl. Very touching and made for children. Maybe it could help you reading this book to your children and talking to them about what they understood, paying attention to hints about their acceptance.
Here you can find Jazz Jenning herself reading her book:
Exactly one year ago I've written an answer to a friend about coming out. It is a little bit different, but maybe you can also find some help in there. I guess what I wrote about parents can also apply to all family members.
You can see it here:
https://www.susans.org/forums/index.php/topic,216768.msg1918892.html#msg1918892Cheer up, sis! You are starting a wonderful journey!! Be happy and be proud!!!
I hope some of these advices can help you to see clearer skies for you to sail out!

Best wishes!!!