Parked car causing fire

Well... cars (and car batteries) are made to not spontaniously catch fire.

Unless if you have electrical issues, but even that is not likely to cause a fire, especially since you have the battery disconnected.

If you want to be extra sure, you can remove the fuel from the fuel tank, but that's probably overkill.

In 35 years, I've never heard of a battery exploding by itself. A battery with the negative removed will not spark.

I've seen a few cars burn, but it was always due to leaking gasoline. If you can smell gasoline/petrol, it is definitely a fire hazard. If not, there is no concern.