Hi Liz, my ancestral line is through sibling Samuel b 1804. I don't know too much about Samuel, 3rd son of Samuel & Margaret (nee Heywood), other than he is shown as the father of my 2nd great grandfather James Thompson 1836-1898. Do you have a spouse for Samuel who would be mother of James?
When searching Robert Heywood on familysearch the result is a marriage of sibling Thomas Richard Heywood Thomson (1814-1876) to Margaret Wilson 14 Mar 1846 at Kirk Braddan not Robert Heywood, which is confirmed by census records 1851 (Scotland) and 1871 (Rhencullen, IOM). Robert Heywood Thomson is shown as having died in Madras, India 21 Jul 1824.
Regards David