Is the sale and purchase agreement made by our brother to sell the heirs' shares at a price of 750,0 per meter valid, given that the price later rose to 1,200,0?

The sale by siblings of their share of a house to their brother can be categorized into three scenarios:

1. If they are adults and of sound mind: The sale is valid. The seller has the right to annul the sale if the buyer is solvent but procrastinates in payment, to avoid the harm of litigation. 2. If they are minors or not of sound mind: The validity of the sale is disputed. Even if it is assumed to be valid with the permission of their guardian, a gift or an unfair discount in the price is not permissible. In such cases, reference should be made to the schools of thought of the jurists. 3. If their guardian sells their share: The sale is valid, but the guardian is obliged to compensate for the difference (25,0 per meter) if he gave an unfair discount in the price. This is because the guardian is obligated to act in the best interest of his ward, and it is forbidden for him to dispose of their money except in a manner that serves their benefit and interest. Any guardian who makes a donation or gives an unfair discount is liable for his actions.