Erik didn't doubt his Chimaeric Demons' ability to replace key figures, even if they were the leaders of foreign countries. In the past, things like this happened frequently, and if the ancient humans, devoid of power, could do that for the Chimaeric Demons, who could shapeshift and assume the identity of multiple people at the same time, it was bound to be even more possible.
The only problem was the Veritas Lenses, but even that had a limited scope of use, especially considering they had a limited range of use. If the Chimaeric Demons played it well, no one would be able to find out they replaced these people.