I found some stories my mother wrote and they were never published. She is deceased. I know I can send them in but can I edit them before I do? She wrote them in the 1960s on a manual typewriter and they need editing. I would want to publish them under her name.
Assuming you either are the sole copyright holder through explicit inheritance, or have the blessing of her other heirs (such as your siblings) to do this, then yes, you can edit her manuscript, have it published under her name, and credit yourself as the editor. See for example the Silmarillion (written by J. R. R. Tolkien, edited by Christopher Tolkien).
In case there are other people who could claim the rights, though, and don't agree with you on this, then you can't either edit or publish the work against their will. This isn't just about money - the copyright holder is entitled to decide whether the work can be published at all.
Absent a specific bequest in her will, the literary rights belong to all of her children — assuming she wasn’t married or that her husband pre-deceased her. It could get quite complicated, otherwise.
When she died, her rights transferred to her estate, so all of her inheritors have a claim moneys from publication — again unless there was a specific bequest or the executor specifically gave the rights to specific inheritors.
Copyright protects the manuscripts from 70 years after the date of your mom’s death. Editing your mother’s manuscript can extend the copyright date. It gets complicated. The estate of Anne Frank extended the copyright past the 70s year limit of her death by giving her father authorship credit since he edited the work, extending the copyright.
Its not a detail you need to concern yourself with at the moment. Its a matter for your literary agent and publisher to understand. You can always pay a copyright lawyer to provide the specifics.