Hi jan,
Ummm...... Rusthall is a little west of Tunbridge Wells, Kent.
Withyham is 5.76 miles SW of Rusthall just inside the Kent/Sussex border. Farnham is way over in West Surrey close to the Hants border in fact from Rusthall to Farnham is 64.57 miles. I can't see where Farnham, 'adjacent to Rusthall' comes in

When I look ar Rusthall on the map I can't see a Farnham anywhere near it & there's no Farnham in Sussex.
Looking for some more on Samuel I found the following likely marriage on the Sussex Marriage Index,
First the licence details,
Archdeaconry of Lewes Marriage Licence, 28 Jan 1829:
Samuel WALTER, bach 21+ brickmaker Rotherfield
Sophia RICHARDSON, sp 21+ Mayfield
Extra Information: SRS 26
Then the marriage. Rotherfield is adjacent to Withyham,
Rotherfield, East Sussex, 29 Jan 1829:
Samuel WALTER, bach otp (lic)
Sophia RICHARDSON, sp Mayfield
Witness wits: Henry BEDWELL; John WOOD
I've looked on the Place names site
http://www.fhsc.org.uk/genuki/REG/ and can't find Farnham in Kent.
I've looked on the Sussex & Surrey marriage indexes & Pallots for a female Walters' to a male Kneller marriage...zilch. Also a quick look at FreeBMD with no luck

Where is this Earl's estate?
Nothing is forth coming for any of the names on the 1841 census, but that's because we've got so little information & there are so many counties involved. My only bit of luck was,
1841 - Wadhurst (next to Rotherfield) HO107/1116/9/15/4
Samuel Walter 38 ag lab
Sophia 32
Sarah 11
William 10
All born Sussex which ties-in with that marriage.
Jane