What is the ruling on paying delayed tuition fees for children through a brokerage firm that settles the amount with the school and collects it in installments with added interest, in the absence of any other alternative?

It is not permissible to pay for tuition fees through an intermediary who pays them on one's behalf and then receives repayment from the student in installments with interest, because this is considered a prohibited usurious loan. There are many lawful means for those who seek them out and strive to obtain them.