Genealogy / finding a copy of a Polish will - SKORZEWO, KARTUSKI region [8]

Hello everybody , my dad was a taken away by the Germans in ww2 and used as forced labour at the age of 16. since the war he has lived in england , but has recently found out that he has an interest in the family farm in the SKORZEWO, KARTUSKI region . Some distant relatives of dads have written to him and asked him to sign over his share of the farm to them . they sent some legal documents that where incomplete, so we don,t know what exactly he is being asked to sign over . The farm is allegedly still registered in his grand mothers name , but was will,d to to my dad and his brothers. My dad has not claimed his share thus far as he only recently got to know about it and his brothers are all deceased.Unfortunately neither myself or my mother speak Polish and can,t help him . He gets upset by the letters from Poland but is too tired to do anything about it . It seems that we need to find a copy of his grandmothers will , and the land registry documents , but we don,t know where to start. Any help or advice appreciated