An act of God would be a lightening strike. A grease fire is not.....that to me is negligence on the cooks part. Propane? Have you followed the recommended periodical inspection of the system? If not....negligence. Electrical? Have there been any alterations to the system? Were they done by a qualified technician? If not....negligence. All sorts of things can be considered negligence. Be prepared for an expensive and long battle in court if you bring the lawyers into it. I too think that each individuals insurance would cover their loss. Talk to your agent and see what he thinks.