How can the expenses incurred for two sisters with special needs be calculated from their own money, taking into account the family's income and preserving the pleasure of Allah Almighty?

It is permissible for the guardian of those in need of care, such as the two sisters mentioned, to spend from their money on them and save the rest for them. If they live and eat with the guardian, it is permissible for him to estimate the value of what they consume in terms of food, drink, services, accommodation, treatment, and clothing. He may take that amount from their pension and save the rest for them. It is not permissible for the guardian to dispose of the ward's money except in a way that benefits the ward, nor is it permissible for him to donate or show favoritism with the ward's money. If the guardian is poor, it is permissible for him to eat from the ward's money in a reasonable manner, meaning the lesser of a wage equivalent to his work or the amount sufficient for his needs, and he is not required to compensate it when he becomes wealthy. However, if the guardian is rich, it is not permissible for him to eat from the ward's money.