Genealogy / Looking for any information about an ancestor - he was buried in a cemetery around Warsaw [2]

I am a US soldier stationed in Germany. I had the good fortune of meeting my wife here and therefor have a German father in law. He had an older brother, a doctor who die in WW2 and is buried in a cemetery around Warsaw. We only know that he died in January 1945. My father-in-law is in his 90s and in failing health, I would like to find his brother's marker and visit the site for him. Hopefully I can bring back some photos for him to remember his brother by. Any help on where to start would be appreciated.