My mom started reading a book our adoption agency recommended for extended family members: In On It: What Adoptive Parents Would Like You to Know. She says she's really enjoyed it so far and that she's learning a lot. She also bought a copy for my siblings to pass amongst themselves. I'm very grateful for the effort she is putting forth to learn how she can be helpful. The littlest things can make the biggest difference.
I haven't read the book myself, but if you're pursuing adoption my mom reccomends it for your extended family:).
And they have a website! In On Adoption.com