sammo there are at least 3 members on ancestry with this couple in their tree, but none of them show anything after 1901, not even the 1911.
I've found a walter holder arriving in sydney in 1914 aged 21 who sailed from London on the Commonwealth, but henry and grace's son walter should have been 2 years younger.
There's a miss Grace L Holder arriving in Hull in 1938 aged 50, on the Largs Bay from Australia, she's about the right age for their eldest daughter.
But like the others there seems to be no recorded arrival or departure, that suggests that your uncle worked his passage with his family, perhaps the eldest sons did too,