What is the ruling on blood money (diyya) and expiation (kaffara) for a driver whose car caused a collision that led to the death of two people from the other car, when the fault in the accident was shared?

Each driver is responsible for half of what was destroyed because both were causes. They are also jointly responsible for the blood money (diyya) of the deceased, to be paid by their respective 'aqila (male relatives responsible for paying blood money). Each of them must also offer two expiations (kaffarat) for the killing. The expiation is fasting for two consecutive months for each deceased person. It is not required for the fasting to be continuous for four months; rather, they are permitted to separate the fasts of the first expiation from the second.