If I am reading your question correctly, you just need an average of all homes sold, not the specific sale price of the home that your family inherited at that time. As another respondent said, I can look up the specific sale price of the home in question if you provide an address.
If you would like or need the report I pulled with additional detail, please feel free to email me at: firstname.lastname@example.org or email@example.com
I will be glad to research that for you, but I need the following information,
1) what is address of the property?
2) Is there any major changes to the property since 1986?
2) What is the purpose of this research, I know that it was inherited property, did you sell the property or do you want to sell the property?
Also, you can reach me at my direct phone or email
I can pull tax data for you if you give me the exact address. It usually shows what the purchase price was that they paid for it. You can email it to me at firstname.lastname@example.org
Otherwise, it's hard to pull data from that far back as the MLS hasn't been around that long.