Presumption of conjugal partnership

Dear PAO,

My aunt claims that the sale made by our grandfather in 1975 in favor of my mother over a certain land was invalid. According to my aunt, when my grandmother died, the property passed to the surviving spouse and her heirs, so her consent was essential to the sale. My mother said that the land was the exclusive property of our grandfather, so he could sell it to anyone. My aunt raised another issue and said that the land was registered in the name of my grandfather, with the description that he was married to my grandmother. She added that such an entry would give rise to the presumption that the property belongs to the conjugal partnership; hence, any disposition after the death of my grandmother will essentially require her consent as a co-owner. Is her claim correct?