For clarity: I agree with you on the highest level, I don't think people committing crimes against humanity should get away with it.
I'm definitely not informed enough (or American enough) to have more useful input than "I don't think whataboutism is the solution". You won't win your extended family over like that, nor any strangers on the internet. Instead suggest ways to actually make a difference, or at least phrase it in a way that you're not sounding like you're making excuses for Trump.