Is preemption permissible between siblings if one of them sells to another?

Pre-emption (Shuf'ah) is the right of a partner to acquire the share of another partner from the person to whom it was transferred for a financial consideration, at the price of the contract. It is not established for siblings unless they are partners. If the objection is about selling a brother's property, this falls under the category of agency (wakalah). The agent is the most entitled to sell, and it is not permissible for him to buy for himself. If the brother has not appointed anyone as an agent, then no one has the right to sell, because it is not permissible for anyone to dispose of another's property without his permission. If the brother is under interdiction, his guardian will manage his property in a way that is most beneficial for him. The guardian of a minor is his father, then his appointed guardian (wasi), then the ruler.