JOSEPH BEN-MENAHEM STEINHART, sometimes spelt also Steinhardt in the encyclopedias,
(about. 1700-1776) was probably the first Jew to use this surname.
His biography has many lacunes, a circumstance that is only natural for the 18th century, when he lived. I came across too many versions of his genealogy, some of them based on mere guesses. I have used mostly and with greater confidence the articles and the information kindly supplied by Dr. Eliane Roos-Schuhl, of Cercle de Genealogie Juive, Paris, which are based in a large experience and most careful research. Also, with less confidence, the respective entries in the "Jewish Encyclopedia" and "Encyclopedia Judaica" and other books.
Joseph was a German rabbi, born about 1700, in the village of Steinhart, which is today part of the Bavarian town of Hainsfarth, Oetingen. He died in Fürth, Bavaria, in 1776. His first incumbency was the rabbinate of Rixheim, and shortly afterward he was elected chief rabbi of Upper Alsace. In 1755 he was chosen chief rabbi of Nieder-Ehenheim in Lower Alsace, and eight years later was called as rabbi to Fürth, where he officiated until his death.Joseph was one of the foremost Talmudists of his time, and questions were addressed to him from Hungary, Italy (Verona), the Netherlands (Amsterdam), and Switzerland. He was extremely conservative, and induced the lord of the manor of Nieder-Ehenheim to forbid men and women dancing together.
In his most important book – "Zikron Yosef" – he calls himself "Yoseph, son of Rabbi Menahem", from Steinhart (in Hebrew "me-Steinhart). Apparently, a certain Hessel, son of Maenel from Steinhart, was his brother. Hessel is mentioned as having married Mundel ? in 1758, in Krautrergersheim, and a second time, Leye ?, in 1760.  It is possible that Manael is another form of Mendel, the Yiddish equivalent of Menahem.
Joseph had a sister, by the name of Yitle, who married a certain Shimeon, born in Hainsfarth, Oetingen. Their son, Menahem Mendel ben Shimeon, (1768–1825), studied under his uncle Joseph, and became also a famous rabbi. In honor of his uncle and teacher he adopted the same surname Steinhart. The name of his parents his reported by him in his response book "Divrei Menahem" (Offenbach, 1804)
Joseph and Yitle, had two more siblings: Seligman and Sorle.
Sorle married Wolf Schnaittach, and died in 1782, in Fuerth.
It is not clear to me if the siblings of Joseph also used the surname Steinhart, or if it was only attributed to them by certain authors, in association with their brother's work.
Joseph ben-Menahem me-Steinhart married three times. His first wife was Chaja Kohn Spira, daughter of Akiba Kohn Spira, with whom she had a daughter, Lea, the wife of Rabbi Yitshak Aron (Yitshik from Pfalsburg). Chaja died 15 December 1754, in Fürth. One source says that her tomb is in the cemetery of Rosenwiller. Rosenwiller never had an organized Jewish congregation nor a synagogue, but had a Jewish cemetery which still exists.
His second wife, according to Benjamin Angel's genealogy, was Rösel Berlin. It is not clear, at least to me, if Rösel was a sister or a relative of Joseph's third wife, Kreindel Berlin (sometimes referred to as Grendel), nor when was he married with her, because he married Kreindel in 29 December 1755, one year after the death of his first wife.
Kreindel, the daughter of Judah Loeb Berlin, from Einsenstadt, Hungary, was a learned person by herself, and her sayings on the Torah are quoted often. Her husband, Joseph ben Menahem pays tribute to her in his books, and gives her credit for encouraging him to publish them. Kreindel died in 1775, in Fürth.
When she married Joseph me-Steinhart, she was already the widow of Yehiel Pressburg, (Yahael) from Ansbach. She was his third wife.
By Kreindel's sister, Merle, Joseph Steinhardt was the brother-in-law of another famous rabbi, Naftali Hirsch Katznellenbogen (Hirsch Moishe), of Schwabach. Merle was Naftali's second wife.
Joseph ben Menahem me-Steinhart was the author of: Zikhron Yosef (Fuerth, 1773), responsa and rulings on the four divisions of the Shulhan Arukh, with an appendix of his novellae and sermons: Mashbir Bar (1828), commentaries on the Pentateuch; and Ko'ah Shor, novellae to Bava Batra. The last two works were published by his grandson, Akiva Steinhardt, the rabbi of Kubin, Hungary. He declined to give a ruling on his own authority in difficult problems, emphasizing that he was one of "those apprehensive of giving rulings," and suggested that the concurrence of authoritative rabbis be sought (Zikhron Yosef 39a–b, 65b, 77b, et al.). He took a firm stand on fundamental issues that were likely to undermine morality and religion. He was especially opposed to mixed dancing, and stressed in his responsum that "any rabbi and instructor is obligated to protest and to abolish any type of mixed dancing that is planned for his city during a festival." In the course of his responsa, he describes how he canceled a dance arranged in Niederenheim, even after the Jewish community had obtained permission from the secular authorities (22d no. 17). In the introduction to his responsa he inveighs against the Shabbateans, and particularly against the Hasidim. Because of his inimical attitude toward them, the Hasidim took steps to have those sections of his introduction directed at them removed, and in many editions the whole of the introduction is indeed missing.
Steinhardt mentions that he was "greatly punished by the death of children and grandchildren... and few of many remained to him." His son MOSES (d. 1799) was the author of a Judeo-German commentary to the Sha'ar ha-Yihud of Bahya's Hovot ha-Levavot (Fuerth, 1765).
STEINHARDT, MENAHEM MENDEL BEN SIMEON (1768–1825), rabbi and author, was a nephew of Joseph Steinhardt, by his sister Yitle and her husband, Shimeon. He was born in Fuerth.
He published his responsa, Divrei Menahem (Offenbach, 1804), while he served as rabbi in Minden, and in the same year he was appointed rabbi of Hildesheim. When the consistory of the kingdom of Westphalia was set up in 1808 in Cassel by Israel Jacobson, Steinhardt was appointed one of its members, together with Leib Meir Berlin and Simeon Isaac Kalkar. They were requested by the government to adopt and formulate the constitution and theology of Judaism on the pattern of the French Sanhedrin established on the initiative of Napoleon. Steinhardt, like the other members of the consistory, aspired to a moderate form of Judaism, an aspiration well reflected in Divrei Menahem and in Divrei Iggeret (Roedelheim, 1812). The latter work was published by his friend Binyamin Ze'ev Heidenheim, who added notes and glosses to the book. Steinhardt was the first German rabbi to omit portions from the liturgy. One of his well-known lenient rulings—permitting the use of legumes on Passover—aroused the vehement opposition of the Orthodox rabbis. He was one of the first rabbis to deliver sermons in German. In 1810 he taught Talmud at the Teachers' Training Seminary in Cassel. In 1813 he was appointed rabbi of Warburg, and in 1815 became rabbi of Paderborn, where he spent the rest of his life.
I owe here an explanation to my readers: the identification I make between the two different spellings – Steinhart and Steinhardt.
In addition to the fact that all the above rabbis are listed in different publications under both spellings, I have noticed the signatures of Joseph ben Menahem, both in German and Hebrew in a document published by Dr. Eliane Ross-Schuhl in her article quoted in the endnote.
Here is the part of the article relevant to our issue:
While in Hebrew here signs Steinhart, with only a "Tet" (see explanation in my Introduction ), in German it seems quite clear to me that it has a "dt".
Steinschneider, Cat. Bodl. col. 1533;
Carmoly, in Revue Orientale, iii. 307;
Frankel, in Orient, Lit. viii. 246.
Loewenstein, in: JJLG, 6 (1908), 190–9, 218, 222f.;
Y. A. Kamelhar, Dor De'ah (1935), 90f.;
R. N. N. Rabinovicz, Ma'amar al Hadpasat ha-Talmud (19522), 123f.
Graetz, Gesch, 11 (19002), 280f., 375;
Zunz, Ritus (19192), 171;
Lewin, in: MGWJ, 53 (1909), 363; Lazarus, ibid., 58 (1914), 185f., 459–82, 542–61.
 A.A. Fraenckel, "Memoire juive en Alsace, contrats de marriage au XVIIème sicleª. Strasbourg, éd. De Cédrat, 1997 –' quoted by Eliane Roos-Schuhl, in her article ªDe Joseph Steinhart, grand rabbin d'Alsace, aux Levy, +ère et fils, banquiers" – Cercle de Génealogie Juive, Nº. 52, Tome 13, Winter 1997.
 L. Rosenthal "Der Hanauer Rabbiner Moshe Tobias (Rav Moshe Tuvje" Sondheimer (1775-1820) und seine Nachfaren in der Ehenaliger Frankfurter Metallfirma von Weltruf Beer, Sonderheimer" (Hanau, 1975) By Courtesy of my friend, Dr. Benjamin De Vries.