Awliscombe baptisms dont seem to be on line.
Death of Isaac is 1846 aged 51, so born 1794/5, Awliscombe near Honiton, so not far away, he was a carrier so could have come from any of the parishes around Woodbury.
might be worth investigating the couple you found to see if they are still alive in 1841/51 and how old they were. Could have married young and he could have been the youngest of a large family.