There are several different ways you can go about valuing the house. The most common ways are to get a formal appraisal, broker price opinion, comparative market analysis, property tax assessment, or use an online price estimator such as Zillow or Redfin.
It is important to know the real value of the home before deciding how that would be divided.
If the house is going to be sold and the property is going to be divided equally or in some sort of a share in the short term it might be less important to know the actual value if it is going to get sold relatively quickly.
