in rem: Lat. Actions against a thing (res) and not against a person. A lawsuit in rem involves settlement of a property claim without reference to the individual claimants. This judgment is binding on all claimants to the property, whether they are parties to the action or not.
This likely means that you and your husband would not be liable for any money the taxing authority may win (unless the authority has some other basis for a judgment against you).
The contractor likely fails to pay property taxes and the authority is taking legal actions to seize the property for the taxes.
If "[you] have no idea what [you] are responding to", you likely should review your specific facts with attorneys local to the court proceeding to that you see what legal options are available to you.