The Iowa Interstate and RJ Corman QJ's are Chinese, so as Walter mentioned, the engineer is on the left and the fireman is on the right. For US built engines operating in the US, it's engineer on the right, fireman on the left. In the UK it varies by the railroad, although engineer on the left seems to be more common. In Europe it's the same as in the US.
Many larger US engines had two seats on the left, one for the fireman and one behind him for the head end brakeman. On large vestibule cab engines, such as the Ohio Central 6325, there were drop down seats behind the cab doors so there were two seats on each side. This would be for one or two brakemen.
In steam days, the conductor was in the caboose or back in the passenger train. Today with two person crews on trains, the conductor rides in the engine and sits on the left in what used to be the fireman's seat, while the engineer sits on the right.