I have occasionally found names get a bit changed.
But I suppose you've also looked for him under things like Aid, Adey & Addy?
Having looked again at the Brighton deaths, they may help explain why no one else seemed to tie to John's family, for it is possible that several siblings had died by 1846 when he was arrested.
Deaths 1843 ADE Maria (mother or sister?) Brighton
Deaths 1844 ADE Ann (sister?) Brighton
Deaths 1846 Ade Lucy (sister?) Brighton
Deaths 1855 Ade Maria (mother or sister?) Brighton
If most of the above were his family, why did they die and was John placed in the parish workhouse in Dyke Road?
Genes Reunited has someone that possibly ties in with John's sibling, Eliza Ade of Brighton. Their Eliza Ade married in 1857 to a George Slater and had daughters called Maria & Lucy, the names of her two possible deceased sisters. The birth year the GR subscriber has given for Eliza is 1839, but there is not a FreeBMD entry that matches this and the censuses suggest she could have been born up to 2 years earlier. If they are connected, in 1861 they are living at 25 Blackman Street, Brighton with 3 y.o. Maria A and 7 m.o. Lucy. In the 1971 census 33 y.o. George is a painter living at 13 Marshall's Row, with 32 y.o. Eliza a laundress and in 1881 they are living at 7 Wakefield Rd Brighton.
By the way. I now think the Marylebone connection was just a coincidence that could have led to a false trail.
Roy G