Hi Wendy , note you have been on various sites with other people searching the same family. On a site called "we relate" , it gives Hugh & Ann Leece as Robert's parents and Thomas Quayle & Elizabeth Williams as Elizabeth's parents.
Although you did not give me Thomas in your list he appears to be twin of Elizabeth b 1826, so this would give credence to that idea.
Elizabeth , daughter of William and Isabella Quiggin can be discounted as she married John Watterson in 1825.
I have severe doubts on Robert's parents as there are no Hughs or Ann's in the childrens names.
Searched for wedding of Elizabeth Knickle (using Frances thoughts) to try to discount her , but could not find one , however a William Shimmin & Elizabeth Knickle had a daughter Marianne in 1835.
Hugh and Ann had 10 children and named 3 after their parents , they did not name them in "order"
One other doubt is a Robert Cubbon , with father Hugh , a widower married Margaret Quayle a widow 16/11/1854 in Marown , I cannot find another Robert Cubbin that fits for this one. Hugh is vary rare name on the IOM.
The WeRelate site states James died Victoria 1915 and his brother Thomas (not on your list) also died Victoria , but in 1902.
I assume you have Robert & Elizabeth's death certificates and there is no detail ?
Cheers
David