But your family member don’t represent Belarusian population. So when you writing it’s not surprising to find a Finnish looking in north-western Belarus is not accurate. Lithuanians of south-eastern Lithuania don’t look Finnish either. I am not a mix of Russian, Polish and Ruthenian too. I am Belarusian by descent .
Here’s anthropological map featuring Estonian, Latvian, Lithuanian, Finnish, Belarusian and two western Russian (on border of Belarus and Latvia). The plots is based on large samples featuring 20 physical variants prepared by anthropologist Deryabin from Moscow State University.