How do I convince my friends that not all Germans/Austrians are Nazis?

I have two friends (twins) who are Jewish. Something like 47 members of their family were murdered during WWII by the Nazis. Recently both boys have convinced themselves that all Germans and Austrians are responsible for this. It's really ironic that they are bigoted against people for supposedly being bigots! Especially since one twin is close friends with an Austrian boy. I have a crush on that same Austrian boy and have been accused of being antiSemetic and a neoNazi! How can I convince them that this generation of Germans/ Austrians is not responsible for the Holocaust, and not blow up at them? I've pointed out that these boys are part German- no, they're not, apparently they're 100% Middle Eastern because their German relatives only married other Jews (Hasidim). I also asked if 10 year old Germans are responsible- they said yes. I told them that my ancestors were slave-holding b@stards and apparently I'm responsible for that too! Then I just got REALLY mad...So how should I make a couple of angry teens see how crazy they are being? What's a good argument to make? Ugh, sorry for my rant.