2 train crews in one?

the other day down in plainfield, illinois which is the beginning of the canadian national (ex. elgin joliet and eastern railroad) illinois river subdivision and there were two elgin joliet and eastern locomotives coming through and in the front locomotive there was a conductor and engineer and I had notied that in the second engine right behind the lead there was another train crew which I realized that down in goose lake where they do all there work the first train crew known as JSW1 would be relieved by JSW2 after 5 hours of work down there and was wondering was the other train crew in the second locomotive the relief crew, also if they were what would they be doing for 5 hours just waiting in a train or doing something else?