Your Grandparents were "liberated" from the Nazis by the Russians if they were living in Poland. They must have had an interesting time getting out before the iron curtain fell.
As you know, the Russians "liberated" the vast majority of the European continent including a large chunk of Germany. FDR and Churchill were in a real pickle because with Russians occupying most of Europe and given their vast commitment to the war, they were in a difficult negotiating position. THere is conjecture that Churchill wanted to drop a few nukes on Russia at the time to enforce new terms but FDR, as sick as he was and trying to bring a close to the war on Japan was reluctant to open a new western front.
Most historians would argue that it is Russia that won the war in Europe, not the US. The US assisted in bringing the war to a quicker end in Europe but the writing was on the wall.