I looked at the Tour the Maranoa site - Roma has a Chinatown? Now that suggests mining of some sort - but gas wasn't discovered until 1900. Perhaps they were engaged in quarrying for the railway. Roma was, at one time, a major railhead catering for the rail transport of cattle which had been brought on foot from a vast area.
Queensland was in drought from 1867-68 plus 1. It would have been a time when large numbers of cattle were being moved out of the area or sold off. Perhaps, as Lyn suggests, there may have been some link between Ambey Downs and Liverpool, or perhaps your ggg-parents simply saw an opportunity to make some money.
Do you know the occupation of Edward? That might give you some clues. Also, what was happening in their lives at the time? I imagine that two sisters married to two brothers would promote very strong bonds of support between the two couples. Or perhaps it was just a family visit.
Whatever ... I'm still astounded that women had the energy, determination and guts to pack up the kids and the cooking equipment and travel these enormous distances. Makes me feel like a total wimp.
