MechEngr
It's always so tempting, when some specific legal issue is in the public arena, and someone deliberately muddies the discussion, to wish upon that person the best counsel they can find if and when they find themselves in court. But this being a community, instead, I'll say I hope you never even need legal counsel at all.
The subject is the DPA. If there's a problem in the international legal framework which precludes justice - as someone may define it - with respect to the country, Ethiopia, that isn't an argument that will help in the DPA matter. It may arrive as a surprise, but legal counsel representing the families have an obligation to represent them as fully and far as the law allows. What can or cannot be achieved under current law in holding Ethiopia, the country, accountable, just isn't a factor. (If it turns out that the 5th Circuit case, the appeal of the DPA status, does involve the Ethiopian government issue you've asserted, I'll come back here and acknowledge it.)
I won't even guess at how the domestic law of Ethiopia would handle a lawsuit against the government. Maybe that's a subject you're well-versed in - but I'm not and won't guess as to how the U.S. doctrine of sovereign immunity might find a parallel in the other country.
As to the flight operation itself of ET302 - strictly off-limits for this SLF/attorney, so I'll leave it alone, other than to say your comment certainly seems to blame the pilots, though unclear how that blame compares in your view to others at fault... like Boeing. But as a non-aviator, I'm not commenting in substance on all that.