Negative gearing is just the ability to offset losses - just like any other business.
first home buyer grant - put in to cover the increased cost of buying a home due to the introduction of the GST. As the name suggests only available to first home buyers no one else.
first home renter grant - Actually this does exist in a way it is called "rent assistance" for low income earners. Also here in SA we have HousingSA - they will provide low income earners with a bond and if it is their first time a couple of weeks rent as well.
"those two are just the beginning if property starts to fall"
If you honestly think the government would mess with either of these things if property really starts to fall you are deluded. Despite the governments overall incompetence they will not want to make the market worse - at best they would only consider removing these if the market was in a stable or growing condition.