Yes, I assumed NuPavel is the older brother who doesn't exist in Day of the Dove.My assumption on prime/nu Chekov is that in the Kelvin timeline, Andrei Chekov got leave at a different time, and hence he and his wife had their first son a lot earlier, but still gave him the same name. The prime Chekov is the younger brother, who never had an older brother, IYSWIM.