Give me the dates you have in mind and I'll check with ET for you. Bear in mind that the flight to IAD stops in FCO. So as always contingencies are in order. You may want to look into connecting via a European city where they don't require transit visas for Ethiopian citizens. You'll just be staying in the transit zone and would have a bigger choice of flights/carriers to you arrival city in the US. Congratulations and all the best with your family