Can your cousin sell you his land at a lower price, provided that he and his mother continue to benefit from it until their death, in order to preserve the land for his mother?

It is not permissible to use stratagems to disinherit an heir, which is known as tawleej (deceptive transfer of property). It is not in the character of believers to evade Allah's rulings through deceptive means that invalidate justice. The Permanent Committee for Scholarly Research and Ifta has forbidden the act of entering into a tawleej contract to disinherit heirs and has warned against pursuing a path for which one will be punished.

Therefore, it is not permissible for your friend to sell you his properties through a fictitious sale to disinherit his paternal cousins. Rather, he should entrust his affair to Allah, and his mother will inherit one-third of his estate if he dies before her. Allah Almighty has commanded those who fear for their weak offspring to fear Allah and not to resort to stratagems to circumvent a right that Allah has ordained. So, let your maternal cousin fear Allah and leave the division of his inheritance as Allah has commanded.