I've been able to trace what happened to the first six girls through newspaper items, records of their marriages and deaths, and in the case of Susan and Eliza, their appearance with their soldier-husbands in British censuses. But I've never been able to discover anything for certain about Jane and Bridget.
Perhaps they were taken in by another family, as Susan's daughter Harriet was, and in the process their names changed. That would make sense if Catherine was struggling to raise so many children. Or maybe they died, unrecorded, in childhood. It's also possible that they married in another state, but I haven't come across any marriages with enough information to identify them.
The South Australian Register of Monday October 1, 1877 carries this intriguing snippet of news:
Jane Mason, single woman, was charged, on the information of T. Boddington, licensed victualler, with disturbing the peace of the Shamrock Hotel, Currie-street. Mr. W. V. Smith defended. Fined 5s.
If this was the same Jane, she certainly wouldn't be the only Mason daughter to be charged with disturbing the peace! But there were several Jane Masons in Adelaide at this time, and there's nothing here to identify this Jane as being Catherine's daughter. As for Bridget, I can't find any newspaper mentions.