It was consistent with common practice to name a child in honour of recently deceased grandfather Loebel Cassirer (1745-1809) .

The assumption that Gersen, Hirsch and Jacob Loebel Cassirer are sons of Loebel Cassirer (1745-1809) and then their offspring - namely from Gerson (Simon, Loebel and Serel), from Hirsch (Lazarus, Leser, Serel and Loebel)) and from Jacob (David) - are so related is an assumption, reasonable in relation to the chronology but unproved until more data is available.

From Irene Newhouse (email “Breslau Cassirer biriths, 1805-1812” sent 9 Aug 2005):

 I remembered that one of the Mormon films, 1184380 was  extracted by Stephen Falk & Werner Zimmt & Stephen sent me the Excel spreadsheet.  Here are all the Cassirer births from it.  The fields are: ordinal # in register, child's name, surname, father's given name, mother's given surname or patronymic, mother's given name, date of birth, page in register.

48 Joseph CASSIRER Moses Loebel SALOMON Pessel 5/7/1805 12
61 Simon CASSIRER Gerson Loebel MENDEL Rebeca 8/6/1805 16
5 Lazarus CASSIRER Hirsch Loebel ESIAS Rosel 10/19/1805 21
48 Jochem CASSIRER Moses Loebel SALOMON Pessel 8/3/1806 31
39 David CASSIRER Jacob Loebel DAVID Schoncke 8/5/1807 43
12 Leser CASSIRER Hirsch Loebel LESER Hadas (?) 1/4/1808 49
63 Loebel CASSIRER Moses Loebel SALAMON Pessel 7/3/1809 82
28 Loebel CASSIRER Gerson Loebel BERGHEIM (?) Rebeca Mendel 1/15/1810 92
93 Serel CASSIRER Hirsch (none) Hadas 5/5/1810 110
45 Loebel CASSIRER Hirsch Loebel LAZARUS Hadas 6/27/1811 123
60     Jacob CASSIRER Moses Loebel SALAMON Pessel 8/16/1811 127
57 Serel CASSIRER Gerson Loebel BURGHEIM Rebeca Mendel 5/22/1812 144

(note that "middle" names are actually patronymics, so that Moses Loebel, Gerson=Girschel Loebel, Jacob Loebel & Hirsch Loebel should all be brothers, unless there were 2 Loebel Cassirers in the previous generation [not all that likely, plus we've got the Family Book list indicating same].

There was no birth in 1812 corresponding to Siegfried Cassirer, so I'm guessing in this list are the 3 middle sons whose names you didn't know.  I'd have expected Siegfried to have been named Scheftel, Samuel, Saul or Salomon at birth, incidentally.