Hello Wolfgang
Having trouble getting my head around it all, but it looks to me to be the same Hermann Otto Grunwald that has perhaps married two Louisa's. Louisa Tatzke c 1861-1936 and Louisa Blinco 1872-1944. I have the year of marriage of Hermann to Blinco as 1928, and have not been able to find when he married Tatzke (this could be spelt with many variations). Louisa Blinco is related by marriage 9 steps from my husband so I am afraid I do not have any further information on her or Hermann. You could try the Toowoomba Historical Society http://www.toowoombahistory.org.au/ We have found the local history societies we have approached to be most helpful.
I do have family connections to Prussia, having descended from Karl August Hempel 1812-1900 who arrived in Australia in 1858 aboard the 'Dorothea' from Hamburg. I have been lucky because there are a lot of people researching and publishing information and photo's on the extended Hempel family.
Good luck with your research and I will certainly let you know if I happen upon any further information which may help you with Hermann.
Regards
Jeanette