Oh my what a beautiful GFG! My favorite quilt pattern! I am working on my 3rd one at the present time. I have never really cared for the ones I have seen that were machine quilted, but yours has surly changed my mind. You have done such a beautiful job. You are so lucky to have your sisters to work with.
I have used Hobbs 80/20 batting with much success. Not sure that would change the weight however.