Real Estate / Land value and ownership in Poland [6]

My grandfather and grandmother owned 7 hectors of farm land in Poland. My grandfather died in 1947 his ownership was split between his 3 children from his first marriage (1st wife passed away), his two (2) children from his 2nd wife (my grandmother) and my grandmother When my grandmother died in 1967 her ownership went to her two biological children. No one knew about this land in Poland until my grandmother's sister passed away in 1994 Poland and her daughter requested power of attorney over the land to collect the rents and pay the taxes. In 1998 my step aunt and my mother went to Poland and gave another relative limited power of attorney to collect the rents and pay the taxes. In 1999 she again went to Poland (this time with her sister-in-law and her biological brother) to appear in the Polish court with all the requested documents. She also hired a Polish attorney, who did nothing for her. This has been going on since 1998 . She wants to sell the land. The tenant farmers who are working the land are interested in buying the land (4 tenant farmers are involved) She needs to know what the land is worth. The buildings on the land are owned by the tenant farmers. All one living step sister (94) and herself (82) (the other have since passed away) own is the farmland. Being that she is here in USA, how does she go about getting the land values? We do have all the address. All farmland is located in Ingolomia