What should we do regarding our inability to pay a blood money (diyya) amount of 35 kilograms and 700 grams of silver for an accident caused by my son?

Your son is liable for the blood money (diyya) of the person killed by mistake, and this blood money is to be distributed among his 'aqila (male relatives on the father's side). He may seek help from others or from zakat funds if they are unable to pay it and the victim's guardians do not pardon him. He is also liable for the expiation (kaffara) for killing by mistake, which is the freeing of a believing slave. If he cannot find one, then it is fasting for two consecutive months. He must also repent to Allah Almighty.