I think these families are definitely tangled together somehow. I found marriage of Robert Moffat and Jean Renwick (14/12/1810) and also the birth of a son to them, David 1816 which appears to have been put on IGI by a private individual (but no details of who)- this David is listed as dying 9/4/1838.My John Moffat also had a son David (1838)(my ggxgrandfather)as well as the one called Robert.
I have also found marriage of a Jean Renwick to James Bryden 4/7/1835 Kirkpatrick Juxta)- she could be a niece of your Jean.My John Moffat had a daughter called Mary Bryden Moffat and until now I have not figured out where the "Bryden" came from. Unfortunately the relevant IGI OPRs for Kirkpatrick Juxta seem to be those which just list female births, but next time I am on Scotlands People I will investigate further and let you know what I find. Trish