Who gets the minerals

Just curious my father signed for mineral rights that was sold by my grandmother. He passed and I know me and my sister share a third with my stepmother. Just curious what happens when my stepmother passes. Does it revert back to me and my sister after she passes or can she will it to her kids? In mississippi

I’m not licensed to practice in Mississippi, but the following may be helpful. https://law.justia.com/codes/mississippi/2010/title-91/1/91-1-3/

What do you mean “my father signed for mineral rights that was sold by my grandmother”? Was he the sole heir of your grandmother?

If I understand you correctly; If you each have 1/3 of the minerals, each of you can pass them on to whomever you want to, usually within your blood line. Are you sure your father didn’t do so, and leave you and your sister each one-half?