Hello Ralph,
After reading the Will of Edward Lancaster mentioned by Leanne
are you sure he stayed in Kent and didn't return to Australia?, or maybe this is another relative.
as there is this entry on the Pre-Release Wills and Probate site for Victoria.
Edward Lancaster Inn-Keeper Castlemaine 26 Nov 1875
I am struck by the co-incidence of name contained..... he left all his estate to his WIFE MARY ANN. He asks for her guardianship of their children whom he does not name.
Now it looks to me like some angles here need a rethink.
If he is the son of your Edward as you say, then even if he was the firstborn.... in say 1859, he is too young to be the father of plural children when he dies in 1875.
Sue