The book states: "Only child of Johann Gottfried BORMANN and Johanna Caroline E Schulz".
So, are Gustav Adolph, Mathilde Wilhelmine, and Wilhelmine Amalie not children of this couple?
If that is the case, why is Gustav Adolph naturalised in South Australia at the same time as his father, and Diedrich naturalised two years later?
I'm not against having Diedrich in the family, I just have no sources for making that claim.
In addition, the birth dates of Gustav Adolph (22 Oct 1820) and Diedrich (1 May 1821) are too close, so if they are part of the same family then one of those dates is wrong.