My uncle died in 2006 and the family house was just sold in 2008. There was no estate because his part of the house was in an irrevocable trust that went to the rest of the family. How can I find the basis for members of the family who inherited various fractions of it on dates ranging from 1963 to 2006? No one has any information about appraisals, etc for any of these dates. I found the property tax bill for 2006, but in California that appraisal (because of Prop 13) is way below FMV.

Was there an estate tax filing made when your father passed away in 2006? The executor of the estate should know. That tax filing would have included a list of your fathers assets, including the FMV of the house as of the date of death.

As for other family members - they inherited their bits of the family house on various dates, and the same answer applies - whatever the FMV was on the dates(s) of death of the people they inherited their piece from is their cost basis. Again, check to see if estate tax filings were ever made on these other estates.

In the end if you can't find thswe documents you may need to hire a real estate evaluation specialist to provide you with an estimate of the FMV.