Is applying for an interdiction on the assets of a father who is ill with a brain hemorrhage, is unaware, and whose older brother controls his money and withholds it from his second and third wives, considered disobedience to parents?

If the situation is as you have described, then you must safeguard your father's money and disburse from it the obligatory expenses for his wives and needy children. If your brother refuses to pay the expenses, there is no sin upon you in raising the matter to the ruler to compel him to pay them, or to place an interdiction on your father's money if there is proof that warrants such interdiction. There is no disrespect to your father in this. It is permissible for a son to place an interdiction on his father if he is extravagant or spends his money on corruption.