In my opinion, first, I would look at real estate tax statements to see if any breakdown there that can be used.
If not, you might want to consult a real estate person. Most accurate would be to get an appraisal of the property with breakdown between the houses and use of land.
Absent that, I'm not sure what else you would do.
**Disclaimer: Effort has been made to offer correct information; but due to the discussion forum limitations, the poster disclaims any legal responsibility for the accuracy of the poster's response**
