Hi Skagway,
The problem that you might have in the 1841 census is that Helen, Thomas and John may all be in different locations in this census
I have looked on Freecen for Helen and found 6 entries. There is one aged 55 working as a servant in Edinburgh. One aged 50 working as a ag lab in Castleton ROX, living with an Adam Telfer (brother in law?) One in Kirkton ROX who is a pauper living alone. Of the other 3, 2 look lke they are still married and one is independently wealthy and living in Paisley, so not too sure if they match.
There is a potential Thomas showing on Freecen (the only one that is the correct age and given as born in Jedburgh). He is an Ag Lab in Ulston, Jedburgh where the head of the family is an Adam Pringle. I cannot find a similar entry for John.
The problem with Freecen is that it is not complete for the UK, so there are parishes and counties missing. In addition (and this is not just for Freecen), there are often inaccuracies in the census returns in that birth places and ages are often given incorrectly (or change from census to census!) or mistranscribed by the enumerator.
Doing a quick search on the OPRs on Scotlands People shows a Jane Telfer born on 27/05/1828 to Thomas and Helen - this will be your missing Jessie (Jessie, Jane and Janet are pretty much interchangeable).
I have had no luck with the marriage of John and Christina however.
Cheers,
Clare