Texas has been a community property state since the 1840s. Dying intestate (without a will) in Texas puts a different slant on things. Because of this, if your grandfathers property (the mineral rights) were owned solely by him, they did not automatically pass to your grandmother. They would have passed 50% to your grandmother and 50% divided equally to their children. If your grandfathers mineral interest was owned jointly with your grandmother, then she would have received 100%.
If we assume he owned them solely, then your grandmother only had 50% to pass equally to all her children. So, your mother would have inherited a % from your grandfather (depending on how many siblings she had, and then an extra % from your grandmother when she passed. It is rather hard to explain without knowing children, siblings, and so forth. The changes should have been recorded at the county courthouse with the probate from each death. And, yes, one is required to file probate paperwork whether there is a will or not, which gives the authority to a person by issuing a Letters of Administration for them to be able to pay bills, sell property, etc to settle the estate.
You keep saying you own the mineral rights, but I suggest you figure out who owns exactly how much before doing anything with or about mineral rights. Each person involved will have to deal with their own interest; you might sell yours, but your aunt or your brother might not want to. And, you can’t sell what you (specifically) don’t own.