— born in Londonderry Twp., Dauphin [now Lebanon] Co., PA:
  7.  Christiana ELY, b. 10 Mar 1786 
  8.  Magdalena ELY [twin], b. 11 Oct 1787 
  9.  (Daughter) ELY [twin], b. 11 Oct 1787; died young
10.  Susanna "Susan/Anna" ELI/ELY [twin], b. 20 Sep 1789 — 1850 Census says b. 1784/5 
11.  Michael ELI/ELEY [twin], b. 20 Sep 1789 
[1789/90:  family moved]

— born in Buffalo Twp., Washington Co., PA:
12.  Martin ELY, b. 25 Nov 1791 
13.  Barbara ELY, b. 1793 
14.  Margaret ELY, b. 1799; m. George DYLINGER
[1813:  Lebanon Co. formed from Dauphin Co.]

Possibly their daughter:
.  Anna ELY, b. 1790/1, PA

Anna ELY is the wife of Benjamin HORN, who is the brother of Joseph HORN, who is the husband of Susanna ELY (above).  In the 1850 Census, Joseph and Susanna are living next door to Benjamin and Anna.

1.  William Henry Engle, ed.  1896.  "Records of Bindnagle Church.—VI." Pp. 230-233 in Notes and Queries: Historical and Genealogical Chiefly Relating to Interior Pennsylvania.  3rd Ser. Vol. II.  Pennsylvania State Library, Harrisburg, PA (republ. 1970, Genealogical Publ. Co., Baltimore, MD; Broderbund CD-19).  On p. 231:

Family of Jacob Knizel. The children of JACOB and ELIZABETH KNIZEL were:   i.  John-Jacob, b. Feb. 12, 1774; bap. Feb. 27, 1774; sponsors, Jacob and Ann Mary Hedderich.  ii.  Christian, b. Nov. 23, 1778; bap. Nov. 29, 1778; sponsors, Michael and Anna Mary Ely. iii.  John, b. Sept. 13, 1781; bap. Oct. 7, 1781; sponsors, Joseph and Eve Carmony.

2.  William Henry Engle, ed.  1896.  "Records of Bindnagle Church.—VII." Pp. 237-239 in Notes and Queries: Historical and Genealogical Chiefly Relating to Interior Pennsylvania.  3rd Ser. Vol. II.  Pennsylvania State Library, Harrisburg, PA (republ. 1970, Genealogical Publ. Co., Baltimore, MD; Broderbund CD-19).

INTRODUCTION... LUTHERAN AND REFORMED BINDNAGEL'S North Londonderry Township. The Lutheran congregation dates from the 1730s. Lutheran Pastors:  Casper Stoever, until his death in 1779; Frederick Melsheimer, 1779-c1784; Casper Hoerner, 1787-c1794; George Lochman, c1795. The Lutheran congregation is known as Bindnagel's, two miles north of Palmyra. Sources: Records of Bindnagle Church, near Palmyra... by E.W.S. Parthemore, comp. Harrisburg: 1866. "The Bindnagel Church" by John W. Early, Lebanon County Historical Society Papers 1(1898): 57-70. Egle published early marriages, baptism, and tombstone inscriptions (Egle, pp. 221-222)...

Family of Michael Ely. The children of MICHAEL ELY were:        i.  John, b. July 8, 1773; bap. July 24, 1773; sponsors, Christian Heckedorn and Mary Meyer.       ii.  Jacob, b. May 4, 1775; bap. May 26, 1775; sponsor, Jacob Wenrich.      iii.  Elizabeth, b. July 23, 1776; bap. Aug. 12, 1776; sponsors, Michael Daniel and wife.       iv.  Mary, b. Aug. 16, 1778; bap. Sept. 6, 1778; sponsor, Jacob Kitzel.        v.  Mary-Catharine, b. April 5, 1781; bap. April 12, 1781; sponsors, John Meyer and wife.       vi.  Mary-Margaretta, b. June 12, 1784; bap. June 27, 1784; sponsor, Elizabeth Betterley.      vii.  Christianna, b. March 10, 1786; bap. March 12, 1786; sponsors, John Oehrley and wife. viii.-ix.  Two daughters (twins), b. Oct. 17, 1787; bap. Nov. 4, 1787; sponsors, George Illinger and wife, and John Held and wife.

It seems odd that Engle missed Michael and Susanna.

3.  LDS.  Family Search: Internet Genealogy Service: International Genealogical Index (IGI).

Susan ELI Christening: 27 Sep 1789, Bindnagle Lutheran and Reformed Church, Derry Twp, Dauphin, Pennsylvania Father: Michael ELI; Mother: Mary Regina Source:  Bindnagle Lutheran and Reformed Church, Derry Township, Dauphin, Pennsylvnia computer printout; births or christenings, 1724-1793 by the Genealogical Dept. of the LDS

Michael ELI Christening: 27 Sep 1789, Bindnagle Lutheran and Reformed Church, Derry Twp, Dauphin, Pennsylvania Father: Michael ELI; Mother: Mary Regina Source:  Bindnagle Lutheran and Reformed Church, Derry Township, Dauphin, Pennsylvnia computer printout; births or christenings, 1724-1793 by the Genealogical Dept. of the LDS

1800 Elley, Michael PA Washington Co. p. 706 32001-2010100
 

.  Census Index:  U.S. Selected Counties, 1820 (Broderbund CD-314):

1820

Elly, M.

PA

Washington Co.

Buffalo Twp.

p. 150

The index shows only one "M Elly," but there were two on the page.

.  1820 Census Index and Digital Images (online at Ancestry.com; Image #2 of 5; extracted by Diana Gale Matthiesen):

1820

PA

Washington Co.

Buffalo Twp.

p. 150/629

M Elly

200011-00011-0-100

These data indicate:

No. & Sex	Age Class	Therefore Born	Individuals Inferred
2 males	9 or under	1810-1820	= grandson = grandson
1 male	26-44	1775-1794	= son or son-in-law
1 male	45 or over	in or bef. 1775	= Michael (b. ca. 1745)
1 female	26-44	1775-1794	= daughter or daughter-in-law
1 female	45 or over	in or bef. 1775	= Anna Maria (b. ca. 1754)
1	person engaged in agriculture

It appears one of their married children is living at home, with their spouse and two sons; or, it could be live-in hired help, and the two boys are theirs.

.  LDS.  Family Search: Internet Genealogy Service:  AF - Ancestral File (online at FamilySearch.org).

.  Raymond Martin Bell.  1984.   The Ely-Ealy Families of Washington County, Pennsylvania and their German neighbors; Dennis, Horn Sticker, Wolf.  Self-published, Washington, PA. 14 pp. (LDS FHL 929.273 A1 no. 4775).  Not seen.

.  The Raymond Martin Bell Anthology.   "The Families of George Ealy, East Finley Township, and Michael Ely, Buffalo Township, Washington [County], Pennsylvania" (online at the Washington Co., PA, GenWeb site).  Michael's will signed 13 Sep 1816, probated 24 Dec 1819; settlement 1834.  Says Michael came to Buffalo Twp. in 1790 and died there in 1819, father of 14 children.

.  WorldConnect / Ancestry World Trees (online at RootsWeb.com/Ancestry.com).  Michael ELY is said to have been taxed in Londonderry Twp. from 1779-82.