The members of a family made up of a couple and their children passed away in a gas asphyxiation incident. Are the wife's heirs — her siblings — entitled to inherit her deferred dowry and household furniture? Her husband had bought a taxi and registered it in her name. Based on Islamic law and not conventional law, is this car considered the wife's property which her heirs may inherit?

Article 3 of inheritance law states the following:
If two or more persons die without it being known for certain who has died first, they
shall not inherit from each other. It is irrelevant whether they died in the same accident or not.
Scholars have expressed this as the inheritance of those who die from drowning, in a fire or under a collapsed building. Based on this, the husband and wife do not inherit from each other provided they died simultaneously as mentioned in the question.

The ruling
What the wife has left behind — her deferred dowry, personal property, the car her husband wrote in her name and anything else, is considered her estate which is to be divided proportionately among her legal heirs. This holds true provided there is no legally recognized proof to evidence the fictitious transfer of the car's ownership.