My father died and my mother opted for the usufruct. Today

Yes. In such a case, two solutions are available to you. Or, you sell and you buy back a property in dismemberment with your mother. Concretely, your mother buys theusufruct and you buy the bare ownership of the property. Or, you make him a donation of the sum of money that you receive from the sale of the property so that she re-employs these funds in the acquisition of her future home.