There is one decent ASL book already in braille. it is "A Basic Course in
American Sign Language" by Humphries, Padden, and O'rourke. It is available
from Northern Nevada Braille Transcribers in Sparks Nevada. This is a
somewhat old book that used to be used in a lot of beginning ASL courses
but which is not so popular anymore. The descriptions of signs were, I
believe, put in by the transcribers. Since Northern Nevada is a service
which supposedly prioritizes requests from deaf-blind people, perhaps they
have done another more current book and perhaps it is time someone
requested a more current book if they have not. Also, this book was
obviously printed using a line embosser with tractor feed paper so perhaps
they would be willing to share the Braille files if that was easier for
someone to use.
there are also, surprisingly, a few books done on ASL by Recording for the Blind. I don't have titles anymore, but they shouldn't be hard to find. Each one had pros and cons - one did a better job of demonstrating ASL grammar, another had signs with good descriptions but not much on the grammar of the language. they also have a good number of books that are useful for learning about deaf culture which is in turn useful in learning the language.
The thing is that you really need to get some basics from a live person before the descriptions in the books make sense. One piece of advice I would offer is that while the current thinking is that the best way to learn ASL is from deaf people, for a blind person you might do better if your first tutor/teacher was a hearing interpreter. I learned a good deal of ASL some years ago by hiring tutors - mostly deaf tutors and after years of not using it I have begun again. This time with a hearing teacher. I find that he is much better able to help me understand the way the language works. For example, ASL depends less on signs strung together the way we string words together in sentences and more on creating a space where you put the things and people you are talking about and then reference those places in space. Or on using classifiers which are general hand shapes for people, animals, objects, etc. You might use the specific signs for your grandmother and grandfather to be clear who you are talking about, then use the classifiers for people to show them taking a walk, getting into a car, the general classifier for automobiles to show the car traveling along and then another automobile with your left hand coming out and hitting them. So you would have used only two actual signs for words, maybe a third to show when this all happened, and then tell a story using simple classifiers. I didn't understand this structure when I first learned and I realized now how much it made it hard for me to follow what people were talking about when they really tried to converse with me.