Is it permissible for me to take a monthly sum from my sister's pension in exchange for not renting out or selling my apartment due to her circumstances? Or do I have the right to dispose of my property by renting or selling it without considering my siblings' situation?

The questioner is not permitted to take a fee from his sister's pension, because this constitutes consuming wealth unjustly. This is particularly emphasized according to those who prohibit a guardian from engaging in transactions with the ward's money for their own benefit. The person in charge of a ward's affairs is obligated to safeguard their wealth, manage it well, and dispose of it with caution and in the ward's best interest. As for renting out or selling the apartment, there is no harm in that. The questioner should ensure that the buyer or tenant is someone whose harm is not to be feared. If his siblings object to this, then they should buy or rent it themselves.