All perfect praise be to Allah, The Lord of The Worlds, and may His peace and blessings be upon our Prophet Muhammad and upon all of his family and companions.
The Diya (Blood money) is due on blood relatives male in unintentional and quasi intentional killing; everyone connected to the killer in lineage such as brother, uncle, cousin and even the far bloodline relatives such as the fifth grandfather. In addition, it should be paid and divided among blood relatives male according to their financial capacity and the poor one isn’t obliged to pay any of these expenses.
Nowadays, lineages became very wide and hard to track in some families and people barely know their relatives; thus, they intended to form families’ associations to cover the expenses of car accidents and the like. Consequently, whoever had a relative who was involved in unintentional and quasi intentional killing due to car accidents in which the organs of casualties were damaged is obliged to help in covering the expenses of treatment and the like.
As for other kinds of accidents, participating in paying their expenses is one of the charitable acts similar to helping the distressed and the needy.
Therefore, participating in the aforementioned associations should be on the basis of donating and giving charity, since a person will be rewarded for doing so and burdening similar expenses should be according to an order by which solidarity and justice are maintained among families. And Allah Knows Best.