Is the buyer entitled to rescind the contract and back out of his purchase due to the seller's breach of his condition that the buyer be the sole owner of the property among people?

The summary of the fatwa is that the condition stipulated by the buyer – which is that he has the right to sell the entire property and that he appears to people as the sole owner of the property – is a void condition and it is not permissible to fulfill it, because it is a lie and may result in harm to the seller. It also contradicts the saying of the Prophet (peace and blessings be upon him): "Every condition not found in the Book of Allah is void, even if it were a hundred conditions," and his saying: "Muslims are bound by their conditions, except a condition that forbids what is lawful or permits what is unlawful." In this case, the sale is valid, and the condition is void, because it is among the minor conditions that do not invalidate the contract. Therefore, the buyer does not have the right to annul the sale due to the non-fulfillment of this void condition.