I have amassed a rather extensive list of McKinnells from various sources and I am trying to piece together as much as I can about their inter-relationships. Concerning this particular couple, I feel that there is a non-trivial probability that this Peter is the son of a McKinnell family that is of some interest to me (and until now, apparently no one else). Peter could rather easily be the second Peter (the first one died) of William McKinnell and Janet McCrackan of Kirkinner, Wigtownshire, Scotland, christened May 16, 1797.
Furthermore, in the late 1820s, there was a grocery/tea dealer business in Atherstone (Warwickshire) by the name of "Morrison and McKinnel". I believe that Peter could be the McKinnel in that business as I found 2 children born to a Peter and Jane McKinnell in the IGI... William Henry and Jane Rebecca. As both of these children appear in the Sheffield 1841 census, it's reasonable to presume for the moment that this is the same family. I note that Morrison, above, appears in the 1841 census of Warwickshire, but McKinnel does not...which would fit with his having moved somewhere, presumably to Sheffield.
I'd love to hear from anyone connected with this particular Kirkinner McKinnell family.