I've just been rereading thee posts and I'm not sure what is fact and what is hearsay.
The birth of Alfred Ernest Hopkin in 1911 gives his mother's maiden name as Langley, so we can be fairly certain that the marriage in 1908 between Alfred and Rachel is the right one.
As an aside, the other Hopkin/Langley births in Hull on freebmd are:
Linda R Hopkin Mar 1916
Alice Hopkin Jun 1917
Charles W Hopkin Jun 1918
The Alfred Ernest Hopkin(s) birth at roughly the right time in roughly the right place is this one:
Alfred Ernest Hopkins Jun 1884 Doncaster (not Hull, but quite close)
Eliza Jane may be a red herring as the Ernest Hopkin in the census is likely to be this one:
Ernest Hopkin Sep 1883 Hull ie no sign of an Alfred in his name.
The latest addition is the name Richard. If this is true, then this seems the best bet:
RG12/3864
20 Duke St, Doncaster
Richard Hopkins, 39, gen lab
Elizabeth H, 42, b Kakenham, Norfolk
Thomas H H, 17, lab, b Castleford, Yorks
Richard H, 14, lab
Charles H, 12
Arthur H, 10
Alfred E Hopkins, 7
Archibald H, 5
Florence S H, 1 all others b Doncaster
It all really depends on how you know about Richard.
Not an illegitimate one in sight I'm afraid!
Richard