What is the right due to my brother after he caused an accident that led to the death of a person, knowing that the one who caused it died a week later and the blood money, estimated at 75,000, was paid, and is he obligated to fast for two months as expiation?

If the brother was negligent, excessive, or careless, then the killing is considered accidental homicide, and the blood money (diyah) is to be paid by his 'aqilah (male relatives on the father's side). He must also offer expiation for accidental killing, which is: freeing a believing slave. If he cannot find one, then he must fast for two consecutive months, as Allah Almighty says: "And whoever kills a believer by mistake – then the freeing of a believing slave and a compensation payment presented to his family, unless they remit it as charity. But if he was from a people hostile to you and he was a believer, then the freeing of a believing slave. And if he was from a people with whom you have a treaty of alliance, then a compensation payment presented to his family and the freeing of a believing slave. And whoever does not find [one] – then a fast for two consecutive months as repentance to Allah. And ever is Allah Knowing and Wise." (An-Nisa: 92).