Is it permissible for a mother to sell her share of the house (buildings and land) to her two sons, while her share of the legal inheritance remains for division, and do the daughters have the right to demand the annulment of the sale?

If the mother is a partner in the land and the building, she has the right to sell her share to whomever she wishes, but she must inform the other partners, as they have the right of pre-emption (shufa'a), based on the saying of the Messenger of Allah (peace be upon him): "The Messenger of Allah (peace be upon him) ruled with pre-emption in every undivided partnership, whether it be a dwelling or a garden. It is not permissible for him to sell until he informs his partner. If he wishes, he may take it, and if he wishes, he may leave it. If he sells without informing him, then he has a greater right to it." If your mother did not inform your sisters of the sale, they have the right to demand pre-emption. If the mother sold for less than the market price, this is a preferential treatment for you over your sisters, and your sisters have the right to demand the annulment of the sale. If a dispute arises, arbitration or recourse to the judiciary is necessary.