there are other bapts for John/Jane - he was a member of Atholl St Congregational Chapel and the bapts are there ! - you can check BL's dissenters' baptisms
Clark is one of the many names where some Mormon patron has done a one-name collection then resubmitted them (along with the usual tally of mistakes incorrect guesses as to mother, wrong dates, parishes etc - I wonder if the marriage in Braddan was checked to see what info it gave (I don't think Braddan gave father's names until forced to by 1849 act)
At 27 Eliza would be thinking that she was 'on the shelf' - such often deflated their age in the census - she is Eliza in 41 but age def 23
Mother Margt looks likely to be d/o Hugh/Ewan McGuire + cath shimmin/radcliffe bapt Douglas St Matthews 17891002