Hi Peter , looked to see what I could find for family one . On the late Brian Lawson's site , he has the 1841-1871 , 1891 and 1901 census listed by name , so on the 1841 census , Douglas (town) I found together (the only Robert Douglas on the IOM):
Mary Douglas aged 30 (???)
Robert aged 12
John aged 10
Godfrey aged 8
No matching father . on the 1851 census together in Douglas Town :
Elizabeth 1 month .(birth not on IGI)
Mother Mary has disappeared / remarried ?
There is a christening 14/10/1828 IOM on IGI for Robert Douglas to Robert D and Mary Williamson .
Brian Lawson shows the marriage of Robert Jnr to Mary McCaskie 22/1/1851 .
On the 1851 IOM census there is a Catherine McCaskey aged 50 , in Douglas - different address . Mother visiting after birth ?
Do you have access to 1851 census to check these details ? maybe show where Mary and Catherine born in Scotland ?
Robert , Mary and Elizabeth are not on 1861 census IOM , could not find them arriving in Australia . Do you know when they came ?