Is it permissible for the father to keep $600 for his efforts, while paying the remaining amount to the heirs of the deceased at the current exchange rate, and giving charity with the intention for the deceased among the heirs?

If the father did not volunteer his service to the patient, he is entitled to the customary wage (ujrat al-mithl) for that service, because the absence of an agreed-upon known wage renders the contract invalid. The customary wage is estimated by experts. If what the father took was equal to or less than the customary wage, he owes nothing to the heirs. However, if what he took exceeded the customary wage, he must return the excess to the heirs. This excess is then distributed among the living heirs and those who have passed away, according to Islamic inheritance laws. The repayment should be in the same currency he received, at the exchange rate on the day of repayment, unless the heirs agree otherwise.