All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
1- If your mother has renounced her share in the inheritance to all of you males and females, then giving up this right is considered as a gift from her to all of you. The method of dividing this gift is not up to you; rather, it is an obligation on your mother to be just in what she gifts. So, she either gives the male the same share as the female, or she gives the male double the share of the female: these are the two different views of the scholars on the issue of how to achieve justice between the children when gifting them.
2- The males have no right to build on the inherited land without the permission of the females, even with the intention of giving them their right afterwards. If they do that, they are transgressors and they are required to demolish what they have built.
3- Since the land is small and cannot be practically divided, then it must be sold if one of the heirs requests this, and those who refuse will be forced to sell. The jurists stated that the property that cannot be practically divided must be sold and then its price shall be divided. Shaykh Ibn Taymiyyah said: “Any co-owned property that is indivisible should be sold, and its price should be divided if any of the co-partners requests that. If one (of them) refuses, then he is forced to sell; some scholars of the Maaliki School of jurisprudence reported that there is a consensus regarding this ruling.” [End of quote]
4- If the heirs are forced to sell the land and some of them want to buy the share of others, then he is more deserving of buying it than stangers as Jaabir narrated that the Prophet said: “He who has a partner in a dwelling or a garden, it is not lawful for him to sell that until he is permitted by his partner. If he (the partner) agrees, he should go for that, and if he disapproves of that, he should abandon (the idea of selling it).” [Muslim] An-Nawawi said: “The Muslims unanimously agreed that Shuf’ah (the right of a person to buy the share of the other partner) is confirmed for the partner in the estate as long as it is not dividable.” [End of quote] The best solution in your situation is that you buy from each other.
5- It is not necessary for the validity of the sale that the price be paid in advance; rather, it is permissible that it remains as a debt in the buyer's liability, and he pays it whenever it is possible, provided that the seller agrees to postpone the payment. If the sale is concluded, then the buyer may build on the land whatever he wants.
6- The males have no right to force the females to sell their shares to them, nor do the females have the right to force the males to sell their shares to them. Rather, they agree between them, and if anyone agrees to sell to the other, then this is acceptable.
7- It is important to know, dear brother, that it is absolutely forbidden to use deception and trickery in order to take the share of the females. It is regrettable to notice what is happening in many societies, which still have some customs of Jaahiliyyah (Pre-Islamic Era of Ignorance), where the share of the female is underestimated and males use every possible means to decrease the female's share and only give her very little of it. Hence, we advise the heirs to fear Allah and give the share of the females (i.e. sisters) fully and completely, without tricking them in order to deprive them from their right. Here, we remind you of the saying of Allah (which means): {And know that Allah knows what is within yourselves, so beware of Him.} [Quran 2: 235]
For more benefit, please refer to Fataawa 387523, 309490, 123882, and 130136.
Allah knows best.