Hi
This is rather speculative but a lot of things do fit.
A FORRESTER family arrived in Melbourne on the Loch Lomond
Charles age 34
Mary age 30
Annie age 11
Charles age 9
FORRESTER is not a very common surname in Tasmania but there is a death of a Charles FORRESTER age 36 in 1890 in Mersey, Tasmania which could be Charles senior, and there is a marriage for a Charles FORRESTER in Tasmania in 1901 that could be Charles junior
Hannahs first daughter is Mary Catherine, Catherine I think may have been the name of Stephens mother so Mary could be the name of Hannahs mother. Annie is often interchangeable with Hannah, the age on the passenger list is about 1 year out but that is not unusual
Given the age of the children the family should have been on the 1881 Scottish census but I couldn't find a likely family. I did however find a Charles FORRESTER senior and junior in the same household, Charles senior was the head of household, he had 3 younger sisters and a nephew Charles junior whose mother was probably one of the sisters.
There is also a marriage in Glasgow in 1881 between a Charles FORRESTER and Mary JEFFREY and in the 1881 Galsgow census there is a Mary JEFFREY age 23 with a daughter Hannah JEFFREY age 4. I'm wondering if the FORRESTER family who arrived in Melbourne in 1889 were in fact Charles and Mary FORRESTER (nee JEFFREY) with Mary's daughter Hannah and Charles nephew, Charles junior.
Whilst it is pure speculation the ages fit quite well, Charles junior being raised by a now married uncle would not be unusual nor would a young girl taking her step fathers surname. This would also explain why you can't find a birth for Hannah as FORRESTER would not have been her birth name.
Andy