Is it permissible for me to benefit from my brother's private health insurance for my father's treatment?

If the service is provided as a donation or through cooperative health insurance, it is permissible to benefit from it according to the agreed-upon terms. However, it is not permissible for you to benefit from it if the agreement was that your brother would use it himself, and you should gently explain this to your father. As for health coverage through commercial insurance, it is forbidden due to the elements of gharar (uncertainty) and jahalah (ignorance) it contains. It is not permissible for your brother to willingly subscribe to it. If the company provides him with insurance without his consent, the premiums paid are considered a donation, and he may benefit from the services within its limits. It is permissible to use stratagems to obtain one's right.