I just re-read my note and once again I have Mary/Margaret dyslexia. She was born Mary Gelling, always was Mary and never was Margaret.
In the meantime I've learned a bit more about the children of this Cain family, but nothing substantial. I think it dead-ends with the children (no descendants) unless one of the two daughters that I can't find had issue.

Meanwhile, both Thomas Cains discussed in the thread, born ca 1780 IOM, are without identified parents. Hope they will be found some day.