My parents purchased (lease to purchase) an investment property…

My parents purchased (lease to purchase) an investment property in 1978 together. When they divorced in 1985 their assets were divided and my mother kept the main home while my father was given the investment property which had less than 6 payments left. The property's original owner was deceased and her sister was over her estate and sold the property. Years later it was discovered that there was an error in the deed. The actual piece that was purchased was further back than expected and the original owner and seller had since died. After my father paid off the property he signed a new deed with the incorrect description and it was filed with the court but the property was never listed in his name with the property appraiser.

Fastforward - My father passed in 2010 with no will. From 1985 until his passing he never took the out of the original owners name (don't know why). Now his estate is in probate. My attorney seems to think that since the original purchase for the property was in error because of the description that this property which is valued at $5,000 - .30 acre should not be included in his estate because to correct this error would cost too much (surveyor, etc) and it's worth it and my mom has legal rights to this property still ???? Even though she agreed in their divorce to relinquish any ownership and rights to the property. Their is a history of my father paying taxes on this property since 1985 and I believe his wife is trying to take this property underhandedly. Please advise.