Given the age difference between Sanders and Isabella, we would immediately suspect that Sanders would have had an earlier wife, and the two children born before 1817 support that he did.

"Talitha" is a scriptural word turned into a name, from the phrase, "Talitha cumi," meaning "damsel arise" (Mark 5:41); it is not a nickname for "Tabitha," which is Aramaic/Hebrew for "gazelle."

Willis may be the son of Wife-1 or of Isabella, depending on just when he was born.
  3.  Willis M. THOMPSON, b. 1816/7, KY {33, KY}; m1. Mary MALONEY; m2. Elizabeth COBB

— born in Hopkins Co., KY:
10.  William Anderson THOMPSON, b. Jul 1831; d. 28 Jan 1907, Los Angeles, CA; m. 13 Aug 1849, Hopkins Co., KY, Sarah Margaret BALLARD — sister of his brother Richard's wife, Frances BALLARD

The LDS Ancestral File shows one Sanders THOMPSON married to five women, but in reality these are three Sanders THOMPSONs. 

There are two Sanders THOMPSONs in the 1830 census of KY:  one is our subject, that is, the Sanders THOMPSON (b. 1786/7) in Hopkins Co., KY, who married Ms. __?__, Isabella DOSSETT, and Talitha __?__; the other is the Sanders THOMPSON (b. 1790-95) in Christian Co., KY, who married Margaret "Peggy" BRASHER.  That there is a third Sanders THOMPSON is shown by the fact that both of the Sanders THOMPSONs in KY in 1830 were much too young to be the Sanders THOMPSON who married Eleanor CLARK in 1797 in NC.  Isabella Dossett and Talitha __?__ clearly belong to the Sanders THOMPSON from Hopkins County as they both died in the same county he did (viz., Ozark Co., MO).  The Sanders THOMPSON in Christian County married only once, not twice, to Margaret BRASHER, who is the same person as Peggy BRAZIER. 

1.  Jordan R. Dodd, ed.  1993.  Kentucky Marriages:  Early to 1850.  Liahona Research, Orem, UT (Broderbund CD-229):

Thompson, Sanders	Dorsett, Isabella	17 Jul 1817	Muhlenberg Co.
Cobb, William	Thompson, Mary	24 Jun 1840	Hopkins Co.
Cobbs, Thomas Sr.	Thompson, Frances	19 Jan 1848	Hopkins Co.

2.  Family Quest Archives:  Kentucky Federal Census 1820:  Campbell, Christian, Green, Lewis, Muhlenberg, Nicholas, and Union Counties.  Heritage Quest CD M33-20:

1820	KY	Muhlenberg Co.	p. 135B	Thomas Thomson	301101-21100-0-300
1820	KY	Muhlenberg Co.	p. 141B	William Thomson	100001-00101-0-100
1820	KY	Muhlenberg Co.	p. 142B	Richard Thomson	000011-00010-0-000

These are the only THOMPSON/THOMSON  households in Muhlenberg County; there are no THOMPSONs, at all, in Hopkins County.  Our subject might be living with kin, but none of these THOMPSON households has a couple the right age and a child the right age to be our subjects.  However, the entire Muhlenberg County census consists of only 19 pages (cf., Christian Co. with 104 pages and Hopkins Co. with 64 pages), which suggests that there are pages missing from the Muhlenberg County census.

3.  1830 Census Index/Images (online at Ancestry.com; Image #31-32 of 62; extracted by Diana Gale Matthiesen):

1830

KY

Hopkins Co.

p. 45

Ln. 8

Sanders Thompson

211 100 100 - 111 001 000

no slaves

These data indicate:

No. & Sex	Age Class	Therefore Born	Individuals Inferred
2 males	4 or under	1825-1830	= Son B = Richard (b. 1827)
1 male	5-9	1820-1825	= John (b. 1820/1)
1 male	10-14	1815-1820	= Willis (b. 1816/7)
1 male	15-19	1810-1815	= Son A
1 male	40-49	1780-1790	= Sanders (b. 1786/7)
1 female	4 or under	1825-1830	= Frances (b. 1827/8)
1 female	5-9	1820-1825	= Isabella (b. 1824/5)
1 female	10-14	1815-1820	= Betsy (b. 1819/20) = Mary Ann (b. 1815/6)
1 female	30-39	1790-1800	= Isabella (b. 1797/8)

Did the enumerator err, or is Mary Ann living with her late mother's kin?  (Daughters frequently take a disliking to their step-mothers.)

4.  1840 Census Index/Images (online at Ancestry.com; Image #15-16 of 80; extracted by Diana Gale Matthiesen):

1840

KY

Hopkins Co.

p. 363

Ln. 29

Sanders Thomson

011 100 010 - 001 100 100

0100000

no slaves

These data indicate:

No. & Sex	Age Class	Therefore Born	Individuals Inferred
1 male	5-9	1830-1835	= William (b. 1831)
1 male	10-14	1825-1830	= Richard (b. 1827)
1 male	15-19	1820-1825	= John (b. 1820/1)
1 male	50-59	1780-1790	= Sanders (b. 1786/7)
1 female	10-14	1825-1830	= Frances (b. 1827/8)
1 female	15-19	1820-1825	= Isabella (b. 1824/5)
1 female	40-49	1790-1800	= Isabella (b. 1797/8)
1	person employed in agriculture

5a.  1850 Census Index/Images (online at Ancestry.com; Image #44 of 60):  Liberty Twp., White Co., AR, p. 463, 347/337, enumerated 22 Nov 1850 (extracted by Diana Gale Matthiesen):

S Thompson	63	M			N Carolina
Isabell "	52	F			"

Listed next to daughter, Isabell (æ 25, b. KY, husband J.A. COCHRAN), who is next to son, J.W. THOMPSON (æ 29, b. KY, wife Elizabeth), who is next to son, W.M. THOMPSON (æ 33, b. KY, wife Mary), who is next to son, R. THOMPSON (æ 24, b. KY, wife Frances), who is next to son, W. THOMPSON (æ 19, b. KY, wife Sarah), who is next to Sanders's daughter Mary (æ 34, b. KY, husband W.P. COBB), who is next to daughter Betsy (æ 30, b. KY, husband N. DOSSETT — no, I didn't misread an "H," it is written "N." DOSSETT).  Our subject and his sons are the only THOMPSONs in the county. 

5b.  1850 Census Index/Images (online at GenealogyLibrary.com):  based on the ages and birthplaces of Talitha's children, we should be able to find her still living with her husband in Tennessee.  If Athelia is her daughter (see 1870 census and Athelia's marriage record, below), then Talitha's prior husband should be a Mr. HUTCHERSON (or var.).  I have searched these surnames in the 1850 Tennessee census and examined the page images, without success: HUTCHINSON, HUCHINSON, HUTCHERSON, HUCHERSON, HUTCHENSON, HUCHENSON, HUTCHESON, HUCHESON, HUTCHISON, HUCHISON.

6.  1860 Census Images (online at Genealogy.com; Image #58 of 61):  Falling Spring P.O., Ozark Co., MO, Roll 637 (Book 1), p. 464, PN 58, 385/385, enumerated 28 Jun 1860, official enumeration date 1 Jun 1860 (extracted by Diana Gale Matthiesen):

Sanders Thompson	71	M		Far	600	540	NC
Talitha	50	F					Virginia
James	19	M					Tenn
William	13	M					"
Marsel	11	M					"
Polly A	8	F					"

The children must be Talitha's from a former marriage.  It's unknown (to me) whether the children actually or permanently adopted THOMPSON as their surname.  Listed next to Sanders's son, Richard THOMPSON. 

7a.  1870 Census Index/Images (online at Genealogy.com; Image #11 of 20):  Gainesville P.O., Marion Twp., Ozark Co., MO, Roll 796 (Book 1), p. 215A, PN 11, 69/69, enumerated 16 Aug 1870, official enumeration date 1 Jun 1870 (extracted by Diana Gale Matthiesen):

Thompson Richard	43	M	W	Farmer		350	Kentucky
[Richard's wife and children]
Thompson Sanders	82	M	W	Farmer			North Carolina

7b.  1870 Census Index/Images (online at Genealogy.com; Image #9 of 20):  Gainesville P.O., Marion Twp., Ozark Co., MO, Roll 796 (Book 1), p. 214A, PN 9, 59/59, enumerated 12 Aug 1870, official enumeration date 1 Jun 1870 (extracted by Diana Gale Matthiesen):

Piland James M	34	M	W	Farmer	500	565	Kentucky
Athelia E	29	F	W	Keeping house			Tennessee
John H	8	M	W	at home			Missouri
Mary Ann	4	F	W	at home			Missouri
Daniel W	8/12	M	W				Missouri	Oct
Thompson Telitha	40	F	W	Keeping house		168	Virginia

Some other number was written for Telitha's age, then "40" was written over it, which means she made the biggest fib I've ever seen a woman make regarding her age (she should be 60!).  Yet, her proximity to Sanders and her Virginia birthplace lead me to believe she is/was Sanders's wife.  Athelia is almost certainly Talitha's daughter (n.b., that Athelia was born in TN and so were Talitha's four other children).  Athelia's maiden name was HUTCHERSON/HUTCHINSON (see next source).

8.  Jordan R. Dodd, ed.  1998.  Marriage Index: Missouri, 1851-1900.  Liahona Research, Orem, UT (Broderbund CD-234):

Piland, James M.

Hutcherson, Athelia E.

7 Jul 1859

Ozark Co.

9.  LDS.  Family Search: Census Records: 1880 United States (online at FamilySearch.org):  neither Sanders nor Talitha found, as expected.

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

11.  Archives of the THOMPSON-L and KYChrist-L mailing lists (online at RootsWeb.com).

12.  Messages in the Dossett Family Genealogy Forum (online at GenForum.com).

13.  Email from Margie Williams Garr.