Гавриил, первые трое Уссельманн были родными братьями, получается. Вот информация о них на английском. источник - Днепропетровский архив.


Colonist USSELMANN and his wife Elisabeth (b. 1775) arrived in Selz in around 1809. Colonist Usselmann is assumed to have died during immigration. Elisabeth then wed Johann MILLER (d. 1810), then Ludwig STRAUSS in 1811.
Their children were:
Christian USSELMANN emigrated in Sept. 1809 from Niederseebach, district of Weissenburg, Alsace, France. He was about 19 years old in 1812. He wed the widow Katharina HULM in Selz colony and had two children, Christian (b. 1814) and Katharina (b. 1815).
Jakob USSELMANN (b. 1796) was fostered out to the Strauss family when his mother wed Ludwig STRAUSS.
Martin USSELMANN (b. 1803/04) was fostered out first to the Strauss family and later the FEDER family.
This was taken from a translation of the Historical District Archives, Dneptropetrovsk (Yekaterinoslav)