I've arrived late to this thread! I can add one minor snippet of information that slightly strengthens the picture you've put together, which is that on the marriage cert of Betty Wimbush and Patrick Connaughton, about 1880, Betty's address is given as Gt Ducie St. I don't have the details in front of me, which probably means I should keep it to myself until I do, as my memory is far from infallible, but I won't :-) - I'll check when I get home and post any correction necessary.
In the 1871 census (RG10-4048) Betty is living with her sister Mary and brother-in-law William Davies. So it wouldn't be a surprise if at a later date she was living with a different sibling.
Just thought I should point out the obvious possibility, since no doubt it's occurred to people, but hasn't been stated anywhere yet that I can see, that Martin may actually have been Samuel's son, but because the birth occurred before the marriage he used his mother's maiden name. Of course it may not be possible to prove this one way or the other. I've read elsewhere that there may have been some legal obligation to use one's mother's maiden name in the case of an illegitimate birth, even after the parents marry, though I've no idea how reliable that retrospective legal opinion is.
If you get Samuel jnr's birth cert, I'd also be keen to know the details, if you don't mind. I've inherited a "short form" birth cert for Betty, which has hardly any interesting detail on it. Guess I should order the proper one.
Wonder how Martin came to change profession from butcher to baker - guess he made pork pies

. Never a candlestick-maker, though, apparently...
I hope someone can dig up a marriage record for Samuel snr and Betty snr.
Tim