Children are recorded in The Aussie Census. Someone suggested to me that I try every four years which is when the census is taken, doing this I have found information. Do you have the married names of the three daughters. Usually is it the male name on the census as the head of the family followed by wife and children.
I Suggestion you start with the first national census taken in 1911. Prior to 1911 each state did its own census. Lydia and William married in Queensland then moved to New South Wales each would have done their own census before 1911.I contacted the granddaughter of Primrose,who is Lydia's sister, but she did not do any research outside her direct line.
I also found that the women in the family often used their middle name not there first name and this was confusing for me for some time, not sure it that happened in Lydia family. You can email me stuff if you want and I can have a look my email is
paradies@iinet.net.au. Regards Sharon