How to transfer literary ownership between deceased's estate

my grandmother passed away before publishing a book she wrote, she has two daughters and her estate has been split equally between them. she also didn't explicitly say who would get the rights to her books. one of her daughters is working on and publishing the book and the other said she is not interested in it. My question is, is it necessary for us to ask daughter 1 to transfer her share of the rights of the book to daughter 2 and if so, how do we go about that? can we just ask her to sign a form or is there a more extensive process?