I'm not really an expert
But I have picked the odd snippet up on my Scottish travels
There are 16 Kerrs in Moffat in 1851 (online here...)
http://www.dumgal.gov.uk/historicalindexes/census.aspxAll the older people having been born elsewhere. I find that interesting because it is a fairly common name in Dumfriesshire in general (over 5000 hits on the IGI) so unusual for Moffat not to have any natives.
I've had a look at 1841 on Freecen and there are 9 (or was it 8 I've closed the window!) hits for the name KER which is a common spelling to crop up.
It was common for boys to follow in the footsteps of their parents occupation so if he had a good business they would stick with him maybe. Halifax was definitely a good place to be in the material business, lots of mills.
Another aspect is that many drapers were travelling salesmen so on the night of the census it maybe coincidental that the family are home? All supposition of course. And presuming he was a cloth merchant not a merchant of other dry goods.
I'm certainly not an expert on drapers! But I know it was a guild trade in the past, therefore this may of created a tighter bond between the family if they are all of the same occupation, though guilds where losing importance in the 1800s. But I personally think monopolistic behaviour carried on.
Pam