Brooklyn Daily Eagle, April 29, 1886, p. 1 ("New Buildings")
Checking our comprehensive Park Slope photo archive, we find that the original buildings are still standing. Each of them is three "bays" or windows wide.
The cornice detailing, or what remains of it, matches on two of the adjoining buildings:
An earlier Eagle notice for the same row attributes the buildings to W[illiam]. H. Brown, who may have been in the same firm with George Brown. William Brown was also active in this area of the Slope around the same time:
At the same time George Brown erected his 5th Avenue row, he also constructed a building in Douglass Street, just to the rear. Its completion was noted by the Eagle in the same article that noted the completion of the 5th Avenue row:
It was not unusual for builders to control lots on both sides of a corner, as here. The building is actually only trimmed, not faced, with brownstone:
But the cornice detailing matches that of the 5th Avenue row:
And it is also the only three-story, three-family building on the south side of Douglass Street, which facilitates the identification.
Meanwhile, the four buildings at the northwest corner of 5th Avenue and Degraw Street were erected by Dan Buckley, as noted in the Brooklyn Daily Eagle of March 19, 1887:
Unlike George Brown's row to the north, which is faced with brownstone, the Buckley row is brick with brownstone trim. Again, the quoins on the corner building nicely punctuate the row:
Oddly, the corner building in this block, at 17.5' wide, is much narrower than the other three, which are each 27' in width. The former held only one family per upper floor ("single flats"), while the wider buildings held two ("double flats").