ARMBRUST is a German surname, not a French one; Alsace is an ethnic German enclave in France from which many ethnic Germans emigrated to America. 

1.  Marriage Record:

2.  1870 Census Index/Images (online at Genealogy.com; Image #35 of 58):  Varysburgh P.O., Town of Sheldon, Wyoming Co., NY, Roll 1119 (Book 1), p. 317A, PN 35, 283/293, enumerated 17 Jun 1870, official enumeration date 1 Jun 1870 (extracted by Diana Gale Matthiesen):¤•

Straub Frank	28	M	W	Hotel Keeper	2500		New York
"   Elisabeth	29	F	W	Keeping house			France
Beaver Anna	22	F	W	Domestic Serv't			Belgium
Hoffhauer Philipp	18	M	W	Farm Laborer			New York
Straub John	9	M	W				New York
Beaver Mickael	28	M	W	Farmer			Belgium

John STRAUB was born before our subjects were married; he appears to be the John WEIS in the 1880 census.  Listed five households from Frank's father, Nicholas STRAUB, who is next to Frank's uncle, Barney STRAUB. 

3a.  LDS.  Family Search: Census Records: 1880 United States (online at FamilySearch.org):

Census Place: Sheldon, Wyoming, New York
Source: FHL Film #1254948; NARA Film #T9-0948; Pg 275C
	Relation	Sex	Marr	Race	Age	Birthplace	Occupation	Fa	Mo
Michael ARMBRUST	Self	M	M	W	66	FRANCE	Farmer	FRANCE	FRANCE
Elizebath ARMBRUST	Wife	F	M	W	66	FRANCE	Keeping House	FRANCE	FRANCE
Elizebath STRAUB	ADau	F	W	W	38	FRANCE	Keeping House	FRANCE	FRANCE
John WEIS	ASon	M	S	W	17	NY	Farm Laborer	PRUSSIA	PRUSSIA
Mary STRAUB	ADau	F	S	W	14	NY	House Work	IRELAND	IRELAND

The mistake made by the extractor in the relationship of Widow Elizabeth to Michael & Elizabeth ARMBRUST is seriously misleading (see next source).

3b.  1880 Census Images (online at Ancestry.com; Image #33-34 of 48):  Sheldon, Wyoming Co., NY, pp. 275C-275D, PN 31-32, SD _, ED 210, enumerated 16/17 Jun 1880, official enumeration date 1 Jun 1880 (extracted by Diana Gale Matthiesen):¤•

1880:  for an explanation of the column headings, please see What the Numbers in the Federal Census Mean (missing columns contained no data).

1

2

3

4

5

6

8

9

10

11

13

24

25

26

315

326

Armbrust Michael

W

M

66

/

Farmer

France

France

France

________ Elizebath

W

F

66

Wife

/

Keeping House

"

"

"

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Straub Elizebath

W

F

39

Daughter

W

/

Keeping house

France

France

France

Weis John

W

M

17

Adpt Son

/

Farm Laborer

NY

Prussia

Prussia

Straub Mary

W

F

14

Adpt Daughter

/

House Work

"

Ireland

Ireland

The big question here is whether the John STRAUB in 1870 is the John WEIS in 1880.  We do not find any John STRAUB (ca. age 19, b. NY) in the 1880 census who could be our subjects' son, so I strongly suspect the two John's are the same person, which means our subjects had no biological children.  The fact that John is not listed immediately after his parents in the 1870 census supports that he is not their biological child.

4.  St. Cecilia's Catholic Church Cemetery, Sheldon, Wyoming Co., NY (courtesy of Scott Barvian):

431 - Nicholas' son Frank, d. 1873 age 31 Elizabeth died in 1921 and is buried at the St. Cecilia's South Cemetery about 1/4 mile from the church in a plot with her parents and most of her siblings... The John Wise stone is to its left (Slide 79)...

5.  Emails from Scott Barvian:

According to the notes of a historian who compiled the church records together about 30 years ago, Frank and Elizabeth married in 1865 and adopted a daughter Mary b. 1864, whom they baptized 1871 at St. Cecilia's.  She married John Hyman 1862-1928 in 1890; she died in 1946.  That is the only child recorded... The historian's notebook does not list the baptism of any John Straub or John Weis.  In 1900 John Weis is listed (b. Oct 1863) with my gr-gr-grandparents Frank and Clara Armbrust (Elizabeth Straub's brother). He is listed as a hired man, not a nephew.  His gravestone says "John Wise 1863-1927", and the notebook only says that he lived with Frank and Clara. The Armbrust family emigrated from the village of Riedseltz in Alsace in about 1845.

Scott sends an obituary of John WEIS, which tells us he was born in Pine Hill, Elba, NY, that he died February 8th, that he was the only son of John & Mary WEIS, that his father died in the Civil War, and that he moved in with the STRAUBs when his mother re-married.

6.  WorldConnect / Ancestry World Trees (online at RootsWeb.com/Ancestry.com).