My mother's family lived on Christopher Ave. for many years. Her mother's
death certificate >from 1934 shows the address as 529 Christopher Ave., which I
believe is the address they were at for a long time. The 1920 census has them
at 517 Christopher Ave. Years ago, when my family drove past that area heading
elsewhere, we'd sometimes swing by to see what became of the old home. If I
remember correctly, on one visit, probably in the 1960s, it looked as if almost
all the houses on the block had been torn down, and only my mother's and the
one next door were still standing. These were tenement buildings. The
neighborhood was a terrible slum, and most of the houses (later, probably all
on that block) were torn down for urban renewal. I don't think, however, that
280 was on that exact block- as per my street guide to Brooklyn. But the
houses there may have met the same fate.
You might do better in getting more exact and current info. on some website in
which people reminisce about the old neighborhoods - or perhaps if the local
high school in Brownsville (Thomas Jefferson?) has a website.