You each share one-third of the property. With your older brother, you therefore have a two-thirds majority. This quota is not without interest for a sale, since article 815-5-1 of the French Civil Code provides a solution to the lack of unanimity:
"Except in the case of dismemberment of ownership of the property, or if one of the undivided co-owners is in one of the cases provided for in article 836, the alienation of undivided property may be authorized by the tribunal de grande instance, at the request of one or more undivided co-owners holding at least two-thirds of the undivided rights, in accordance with the conditions and procedures defined in the following paragraphs. The undivided co-owner(s) holding at least two-thirds of the undivided rights express(es) their intention to dispose of the undivided property before a notary, at this majority. Within one month of receiving this intention, the notary notifies the other undivided co-owners. If one or more of the undivided co-owners opposes the disposal of the undivided property, or fails to make this known within three months of notification, the notary will draw up a report to this effect. In this case, the Tribunal de Grande Instance may authorize the disposal of the undivided property, provided it does not excessively prejudice the rights of the other undivided co-owners. The property is sold by auction. The proceeds cannot be reused, except to pay joint-ownership debts and expenses. Alienation carried out under the conditions set by the authorization of the Tribunal de Grande Instance may be set up against the undivided co-owner whose consent was lacking, unless the intention to alienate the property of the undivided co-owner(s) holding at least two-thirds of the undivided rights had not been notified to him/her in the manner set out in the third paragraph."