Sale of conjugal property without spousal consent

Dear PAO,

My grandparents were legally married in 1975, but they were separated-in-fact. Their children, which include my mom, are running after a land which was sold alone by my grandfather to Jose. They are claiming that such sale is invalid because my grandmother did not give her consent to the sale. My Uncle Bo told his siblings that such sale is only voidable and not void. They want to recover the land.