The court as the reference for determining Diyah, its payer and how it should be paid
Diyah should be settled by court, which estimates its value and explains who should pay it. Regarding
Kaffarah (expiation), your brother and the other driver each has to make Kaffarah, which is freeing a believing slave. He who finds this beyond his means must observe Sawm for two consecutive months, that is, sixty days. This is because they were the reason for the death of a Muslim. Allah (Exalted be He) says:
It is not for a believer to kill a believer except (that it be) by mistake; and whosoever kills a believer by mistake, (it is ordained that) he must set free a believing slave and a compensation (blood-money, i.e. Diya) be given to the deceased’s family unless they remit it. If the deceased belonged to a people at war with you and he was a believer, the freeing of a believing slave (is prescribed); and if he belonged to a people with whom you have a treaty of mutual alliance, compensation (blood-money - Diya) must be paid to his family, and a believing slave must be freed. And whoso finds this (the penance of freeing a slave) beyond his means, he must fast for two consecutive months in order to seek repentance from Allâh. And Allâh is Ever All-Knowing, All-Wise.
May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.