I am attached to those Youngs who went out to NY from Liverpool in 1894 because that is the only Charles Young we've found who has any connection (in the censuses) with Islington, Liverpool; and we know that that was the birthplace given on the army papers of 1914 for the man who married Emily Wheeler.
I haven't seen anything yet to suggest that these are different people.
We know that Sidney was born in UK though there is no sign of him at all in the 1911 census. We haven't found any convincing births for Joanne, and no trace of her in 1911 either. And we haven't found any Charles/Emily couples who look likely in 1911.
It seems that Charles emigrated to USA with his family in 1894. We know that his brother Dwight was back in UK fairly soon as he's in the 1901 census but the rest of the family hasn't been found. we just don't know (yet!) if it's the right Charles - but I suspect it is.
So maybe Charles met Emily in the USA and Joanne was born there; maybe other children were born there too. They must have returned to UK prior to Sidney's birth and they were here in 1914 but maybe they went back to the USA, either to live or to visit family, inbetween those dates and missed the 1911 census.
So it would be really good to be able to check out those immigration to the UK records for Charles, Emily, "Jonanna" and Sidney Young that are listed on Ancestry. Until they're checked, I will carry on believing that the scenario I propose above is a possibility!