I think its correct, cupcake.
I think Bethia had a sister, Emma (born c1825) who married an Edward Kidman in 1849. And it was probably this Edward who stated he was the brother-in-law of Bethia. Emma looks to have died in 1874 and Edward remarried in 1875, to Susan Kidman.
I couldn't find Emma in 1841.
GRO BMD refs:
1849 Q2 Marriage - Edward Kidman & Emma Kidman; Biggleswade; 6; 87
1874 Q2 Death - Emma Kidman; age 48 (born c1826); Biggleswade; 03b; 222
1875 Q4 Marriage - Edward Kidman & Susan Kidman; Hackney; 01b; 754
1883 Q1 Death - Edward Kidman; age 55 (born c1828); Biggleswade; 03b; 248
Baptisms - Barton in the Clay
17 Nov 1825 - Emma Kidman; parents: George & Edith
Baptisms - Streatley
04 Apr 1828 - Edward Kidman; parents: Thomas & Mary
Marriage licences:
Reference: P110/1/11/2
Title: Edward Kidman of Streatley, bachelor and Emma Kidman of Edworth, spinster
Date free text: 25 June 1849
http://bedsarchivescat.bedford.gov.uk/Details/archive/110167778Marriage:
married: 06 Dec 1875; St John, Hackney
groom: Edward Kidman; fa; wid; farmer; Clapton
bride: Susan Kidman; fa; spin; -; Clapton
grooms father: Thomas Kidman, farmer
brides father: Thomas Kidman, farmer
witnesses: George Reyn? Thom?ian?, Harriet Field
Probate index:
Edward Kidman, gentleman
15 March 1883; Shefford
late of Shefford in the county of Bedford
Probate 26 April 1883; Principal Registry
George Edward Kidman, of Fenton in the County of Huntingdon, farmer, the son; James Kirkby of Shefford, coal merchant.
£28,199 10s 9d
Probate index:
Susan Kidman, widow
08 Jul 1900
Bridge-house, Shefford, Bedfordshire
Probate 15 Aug 1900; Northampton
Thomas Herbert Kidman, gentleman
£4118 11s 6d
Censuses:
1851 Sharpenhoe, Streatley, Bedfordshire
Edward & Emma, +children
Ref HO107; Piece 1757; Folio 813; Page 13;
1861 Sharpenhoe, Streatley, Bedfordshire
Edward & Emma, +children
Ref RG09; Piece 1015; Folio 37; Page 14;
1871 Edworth, Bedfordshire
Edward & Emma, +children
Ref RG10; Piece 1550; Folio 54; Page 4;
1881 Shefford, Bedfordshire
Edward & Susan, +children
Ref RG11; Piece 1631; Folio 104; Page 14;
1891 Shefford, Bedfordshire
Susan, +children
Ref RG12; Piece 1258; Folio 13; Page 20;
EDIT: Added likely baptism for Edward Kidman