The Polish court is responsible for diving up the assets accordingly
The court divides the estate, not the assets. I'm not sure of the exact proportions (or how close the circle of entitled relatives goes), but the principle means it works out as the OP says above :
so for example the assets are worth 100 then she is entitled to 50 and then 50 will be allocated to his 2 brother and sister and the daughter (just immediate family)
Under Polish law, his partner will be entitled to $$$ and not necessarily bricks and mortar, making it doubly important to get a lawyer in Poland involved, so the cash doesn't mysteriously disappear.