MarkSmith on Family Tree Circles

For at least 20 years members of the MITCHELL side of my family has been researching the MITCHELL family history.
My great-grandfather was Francis George MITCHELL and according to his death certificate he died in Kew, Victoria, Australia in 1946. He was born in Collingwood (c1870) and his parents were listed as John MITCHELL and Bertha Agnes POWER. However there is no record of his birth in the Victorian BDM indexes. He married Daisy Trayes HALLIDAY in 1893.
Going backwards I obtained a copy of Bertha Agnes MITCHELL's (nee POWER) death certificate. She died in Northcote, Victoria in 1913 aged 69. She was born in Westmeath, Ireland (c1844) and came to Australia c1852. She married John MITCHELL in Hawthorn, Victoria aged 18 (c1862). There were 11 children listed on the certificate, including Francis George as the third child. There is no record of the marriage, nor the births of the 11 children in the Victorian BDM indexes. Also we haven't yet found a record of Bertha Agnes POWER arriving in Australia.
However, a member of the family did discover that the last nine children were baptised at St Francis' or St Patricks' in Melbourne. All nine children were listed as residing in Collingwood with the father listed as John MITCHELL but the mother was listed as a Bridget CARBERY! There was no record of a church wedding nor the baptisms of the first two children - John Robert born Sep 1866 and Annie born 1868 (according to family stories) and we have yet to discover anything further about these two. The last nine children were:
Francis George Mitchell, born 1870;
Samuel Power Mitchell, born 1872;
William Walter Mitchell, born 1874;
James Chambers Mitchell, born 1875;
Sydney John Mitchell, born 1877;
Rebecca Jane Mitchell, born 1879;
Joseph Leslie Campbell Mitchell, born 1881;
Hubert Clarence Mitchell, born 1883; and
Mabel Eleanor Mitchell, born 1884.
We have traced forward from these births to find the marriages and deaths and all list Bertha Agnes POWER as the mother.
Turning to John MITCHELL, with no marriage record (possibly listing parents' names) we have been unable to determine what became of him as the list of John Mitchells Victorian Death indexes is quite long. But we think that he may have died before 1913 as the death notice in "The Argus" for Bertha Agnes Mitchell states "... relict of the late John Mitchell...". I have narrowed it down to about 6 possibilities by ruling out some of the deaths using newspapers and probate lists.
Now to the mysterious Bridget CARBERY. There is a record of a Bridget CARBERY arriving in Melbourne on the ship "Boomerang" in Jan 1854:
Thomas Carbery 32,
Margaret Carbery 31,
Bridget Carbery 11,
Stephen Carbery 4, and
Margaret Carbery 2.
This may be the right Bridget CARBERY as she was born c1842, but we have been unable to determine what happened to her. Interestingly I have traced both Stephen and the child Margaret CARBERY and their death records list parents as Thomas CARBERY and Margaret POWER! Is there a link to Bertha Agnes POWER????
There is still a long way to go, especially mapping out the Carberys to try and locate what happened to Bridget as her death certificate, along with John Mitchell's, may hold the key to this family mystery.
I hope that someone out there finds this tale of use and may be able to help.