>>515967108
Don't stress too much.
I oppose blood defilement as any other good man, but Turks themselves are a mix of White and Middle Eastern. A lot of coastal Turks are straight up South Europeans. So if she's already half-German, her non-White percentage is likely quite low, and your nephews will be White.
I'm speaking theoretically, of course. You've seen her, I haven't. It could be that she's an Eastern Turk or clearly Middle Eastern. But I find it unlikely.