Hi Sue,
Thanks for that 2nd opinion on the census reading - you see the problem! Joiner might help point to one of the possible families, tailor to the other.
I was searching in the IGI for children of Thomas Callister & Margaret (-) in that time frame in or around German and the younger children of TC & Margaret Greggor (variations) were a good match. They were married in Nov 1848, after John Callister was born so that led to finding John illegit son of Margaret Greggor in 1847.
John & the other children are with grandmother Margaret Skelly in the 1861 census, and I did wonder where the 'Skelly' came in, thinking it might be a second marriage for the grandmother. Mark pointed to John's mother Margaret Greggor herself being the illegit daughter, born in 1820, of Benjamin Greggor & a Margaret Cowley who did not marry each other. Mark found a marriage for Margaret Cowley and Joshua Skelly in 1833, when daughter Margaret Greggor would have already been 13.