There is an entry on Ancestors Onboard (paysite) for an R Holdcroft - female b 1883 leaving Liverpool in 1913 for Quebec which pretty much ties in with Rosetta's birth year.
http://www.ancestorsonboard.com/HomePageController.action It looks like there was a male Holdcroft b 1911 travelling with her which would fit for son Richard
However - nothing for "Donna" or Robert - but this was Donna's full name
Births September qtr 1908
Gertrude Frances D Holdcroft Kington 6a 515
There is a 1911 entry for a Rebecca Holdcroft b 1883 living in Liverpool but abode is shown as "Institution". However - she married in the June qtr of 1911 in Liverpool
The 1911 index has no other female R Holdcroft apart from Rebecca & Rosetta