Well, after analyzing blurry pieces of the handwriting and studying a map of Poland, I eventually came up with the idea of the place mentioned in the letter. But the letter was sent in 1957! Who knows if the family still lives in the same place? maybe their descendants have different last names? I had some concerns before this onsite research but as some people say, no risk no fun. A few hours later I was there talking to the two older women on the street. As it turned out they lived there all their lives and knew almost everybody in the village.  I was very lucky, the family lived still in the same place. We had a nice chat and as I found out later they were aware of relatives from New Zeland but had no idea how to get in touch with them.  I was extremely happy that I helped them to regain lost contact.