The first shows a Maddigan, Marg't wid. Matthew h 404 Will'by av - the same address as a Maddigan, Jos P, lockfitter.
I haven't come across any other Matthew Mad(d)igans in the Brooklyn City Directory, so it's possible, but not certain, that this Margaret, widow of Matthew, is our Margaret Sullivan Madigan, Matthew Madigan's wife. And it seems that she's living with a brother-in-law, who would be one of Matthew Madigan's brothers. We don't know anything about Matthew Madigan's family, or whether he had any siblings, but it seems possible now that he had a brother named Joseph who was a lockfitter. Their only son was named James, not Joseph, so it's also possible that she's living with him and his name was taken down incorrectly. Knowing little to nothing about the family dynamics, I would think it more likely that she would move in with her son than with her husband's brother (or nephew, I suppose), but that doesn't mean she did.
The second shows a Mulcahy, Mich'l, liquors, 227 Hamilton av, h 85 Luquer
This is Michael Mulcahy. His home is 85 Luquer St, and his business - in "liquors" - is at 227 Hamilton Ave. (Which is just around the corner, according to google maps.) From 1888-1890 (as well as in several other years), 227 Hamilton is the only address listed for Michael Mulcahy and Matthew Madigan is still living at 85 Luquer. Michael and Mary Ann married right around then (October 2, 1888 is the date I have), so they either lived at/above/behind Michael's bar in the first few years of their marriage; moved in with Mary Ann's parents immediately upon marrying, but chose not to list their home address; or moved elsewhere upon marrying, but chose not to list their home address.
We now have proof, or near proof, that
a) despite not appearing at the address in 1900, the Mulcahys had, in fact, moved in there by at least 1897
b) Matthew Madigan appears to have died between 1890 and 1897
c) Matthew Madigan may have had a brother named Joseph
d) Margaret Sullivan Madigan outlived her husband and was still alive in 1897
UPDATE: When I wrote this, I forgot what we already think we know - that Matthew Madigan, in fact, outlived his wife, as evidenced by the fact that he remarried and had a child with his second wife. Second wife was supposedly Johanna Roche, and their daughter was Loretta Madigan. I've never tried looking for that part of the family. I think maybe I will.