ok, I will start with Leonhard's siblings who remained in Germany: Unless stated otherwise all births, marriages & deaths are in Ober-Rosbach
Leonhard Herdt - your family in the US
Dorothea Herdt - no details other than her marriage and death dates in Nieder-Rosbach (you will need to locate the Nieder-Rosbach records)
Maria Katharina Herdt (b 03 Mar 1857, m 04 Mar 1883, d 11 Jun 1939) married Johann Philipp Buch (b 26 Feb 1856, d 14 Mar 1931) (occ Farmer & Smith) - NB there is ancestry in Ober-Rosbach for the Buch family if you require it.
Children:
1. Johann Philipp Buch (b 24 Apr 1884, d 4 Dec 1885)
2. Heinrich Buch (b 4 Oct 1885, m 22 Nov 1908 - note there is no detail of who he married as the records in my book stop at 1900)
3. Philipp Buch (b 24 Jan 1889, m 21 Jan 1917 - note there is no detail of who he married as the records in my book stop at 1900)
4. Anna Elisabetha Buch (b 19 Mar 1890, m 27 Oct 1912 - note there is no detail of who she married as the records in my book stop at 1900)
5. Maria Buch (b 28 May 1895, m 25 Dec 1919 - note there is no detail of who she married as the records in my book stop at 1900)
Anna Elisabetha Herdt (b 19 Jan 1859, m 11 Jan 1885, d 6 Dec 1922) married Karl Franz Hubert Alfred Buschmann (b 30 Apr 1858, d 1 Nov 1914) (occ Mill Owner in Mainz) - there is no information on the Buschmann's prior to Karl, I suspect they came from Mainz.
Children:
1. Heinrich Leonhardt Wilhelm Buschmann (b 23 Nov 1886, m 18 May 1911 - note there is no detail of who he married as the records in my book stop at 1900)
2. Elisabethe Anna Buschmann (b 9 May 1891, m 4 Mar 1920 - note there is no detail of who she married as the records in my book stop at 1900)
Heinrich Leonhardt Herdt (b 11 Nov 1862, d 26 Apr/May 1945 (recorded as two different months in two different locations) occ Miller
m1 26 Dec 1888 Maria Margaretha Welter (b 11 Oct 1866 Nieder-Rosbach, d 21 Feb 1894) - no further info on the Welter's
Children:
1. Heinrich Herdt (b 23 May 1889)
2. Wilhelm Herdt (b 6 July 1890, d 19 Oct 1890)
3. Wilhelm Herdt (b 6 Jan 1892)
4. Elisabetha Herdt (b 29 Mar 1893, d 16 Apr 1948)
m2 22 Nov 1898 Eva Maria Kohlert (b 26 May 1870 Oberseimen, d 22 Dec 1924) - no further info on the Kohlert's either
Children:
1. Elisabetha Herdt (b 2 Dec 1898, m 18 Apr 1920)
2. Emilie Herdt (b 26 Oct 1899)
Hope that helps
Jenny