Is it permissible for the mother herself to use the child allowance for the two children, or must it be sent to help with the expenses of the two children who are being raised by their aunt?

The basic principle is the obligation to adhere to the conditions of the aid and to spend it for its designated purpose. Therefore, this aid is a right for the two children. However, if the mother's sister is responsible for the children's expenses and care, she has the right to this money in exchange for what she spends. If she waives it in favor of her sister (the mother), it is permissible under two conditions: that the mother spends on the two children what suffices them, and that the aid is not more than what is spent on them. If it exceeds that, the excess is a right for the two children and must be preserved for them. If the mother is poor and the children do not need the aid, she may take from it according to her need, because the mother's maintenance is obligatory from her child's wealth. It is important to emphasize the prohibition of friendships between non-mahram (definition) men and women due to the temptation involved therein.