One of the sons is:
.  Daniel KOPP

1.  LDS.  Family Search: Internet Genealogy Service:  IGI - International Genealogical Index (online at FamilySearch.org).

David KUPP  Christening: 14 Apr 1799, German Reformed Church, Stoyestown, Somerset, Pennsylvania Father: Ludwig KUPP; Mother: Elizabeth Source: Reformed and Lutheran Church Records of Somerset County, Pennsylvania. Fischer, Della Reagan

2.  1790 Census Index/Images (online at Ancestry.com; Image #15 of 17; extracted by Diana Gale Matthiesen):¤•

1790

PA

Bedford [now Somerset] Co.

p. 29/257

Ln. 18

Ludiwick Cap

1-3-3-0-0

These data indicate:

Gender and Type	Age Class	Therefore Born	Individuals Inferred
1 free white male	16 or over	in or bef. 1774	= Ludwig (b. 1759)
3 free white males	15 or under	1774-1790	= Ludwig (b. 1784) = Son A = Son B
3 free white females	all ages	in or bef. 1790	= Elizabeth = Daughter A = Daughter B

3a.  Census Index:  U.S. Selected Counties, 1800 (Broderbund CD-312).  Please see my WARNING regarding use of this database (the numerical data have the genders switched). 

1800

Cupp, Ludwig

12010-4301000

PA

Somerset Co.

p. 561

3b.  1800 Census Index and Digital Images (online at Ancestry.com; Image #3 of 3; extracted by Diana Gale Matthiesen):¤•

1800

PA

Somerset Co.

Stoneycreek Twp.

p. 561

Cupp Ludwig

43010-12010-00

These data indicate:

No. & Sex	Age Class	Therefore Born	Individuals Inferred
1 male	9 or under	1790-1800	= David (b. 1799)
2 males	10-15	1784-1790	= Son A or B = Ludwig (b. 1784)
1 male	26-44	1755-1774	= Ludwig (b. 1759)
4 females	9 or under	1790-1800	= Daughter G = Daughter F = Daughter E = Daughter D
3 females	10-15	1784-1790	= Daughter C (b. 1790) = Daughter B = Daughter A
1 female	26-44	1755-1774	= Elizabeth

4.  1810 Census Index and Digital Images (online at Ancestry.com; Image #2 of 4; extracted by Diana Gale Matthiesen):¤•

1810

PA

Somerset Co.

Stony Creek Twp.

p. 430

Ln. 12

Kope Ludwick Ser

11101-11101-00

These data indicate:

No. & Sex	Age Class	Therefore Born	Individuals Inferred
1 male	9 or under	1800-1810	= Son C
1 male	10-15	1794-1800	= David (b. 1799)
1 male	16-25	1784-1794	= Son A or B
1 male	45 or over	in or bef. 1765	= Ludwig (b. 1759)
1 female	9 or under	1800-1810	= Daughter H
1 female	10-15	1794-1800	= Daughter
1 female	16-25	1784-1794	= Daughter
1 female	45 or over	in or bef. 1765	= Elizabeth

5.  Census Index:  U.S. Selected Counties, 1820 (Broderbund CD-314):  not found.

6.  Census Index:  U.S. Selected Counties, 1830 (Broderbund CD-315):  not found.

7.  Anon.  1943-1960.  "Index of Revolutionary War Pension Applications."  National Genealogical Society Quarterly.  Supplement I, pp. 1-1284 (Broderbund CD-210):

p. 614

KOPP (or KUPP), Ludwig or Ludovic, Penn. Elizabeth, W2129

"W2129" is the file number; "W" stands for "widow."

8.  Messages in the Cupp Family Genealogy Forum (online at GenForum.com), one of which messages included a transcription of Ludwig's pension application:

...Ludwic Kopp who on the 18th Nov 1833 personally appeared before the Court of Common Pleas of Allegheny County, State of Pennsylvania, aged 74 years who being first duly sworn according to law, doth on his oath make the following declaration in order to obtain the benefits of the provision made by the act of Congress passed June 7th 1832.  That he enlisted in the army of the US in the month of May in the year 1776, in Allentown, Lehigh Co PA. in Capt. Jacob Haugerbough's company of Riflemen, belonging to what was called the Flying Camp, in the Regiment of Peter Keichlein (or Keathline) and under Major ---bst, Lieutenant John Murray and Conrad Myers, and 1st and 2nd Sergeants John Turner & Abraham Bootzinger, that he entered as a volunteer for seven months, that he served seven months as a private, when he entered the service he lived in Allentown aforesaid .....Penna, he was in the battle of Long Island, and was afterwards taken prisoner at the surrender of Fort Washington, that during the time of his service he marched through the eastern part of Penn. and through New Jersey. He further declares, with reference to the question put to him according to the directions of the War department, that he was born in Northampton Co. PA on the 12 Oct. 1759.  He has a record of his age in an old German psalm book, written by his grandfather in German, his father being dead three months before the declarant was born, but that he has the same and has therefore procured a true copy of the same to be hereto annexed, certified under the oath of Rev'd Kammerer his clergyman, together with a translation thereof...

9.  Anon.  1968/92.  The Pension Roll of 1835: Vol. III, the Southern States.  Genealogical Publ. Co., Baltimore, MD (1998, Broderbund CD-156).  On p. 828:

Statement, &c. of Alleghany county, Pennsylvania.
NAME.	Rank.	Annual allowance.	Sum received.	Description of service.	When placed on the pension roll.	Commencement of pension.	Age
Ludwick Kopp	Private	23 33	69 99	Penn. militia	Dec. 29, 1833	Mar. 4, 1831	75