A neighbor, local photographer Carla Licavoli, saw the plea on the SPP group's site and rescued the kittens.
They are at Hope Vet on Atlantic Avenue between Hoyt and Bond. They are up for adoption! Call Hope Vet at 718 852 4219 if you'd like to adopt on of the three grey kittens.
It may be too late, but this is from a neighbor:
I was walking down 4th Avenue and saw a plastic box with three kittens
in it. The super could only indicate that they were left to be taken by
whoever. I called animal control and they said that I would have to
take them to my home before they could come to pick them up. I am not
able to bring stray animals into my home because of our newborn.
PLEASE, if anyone can help to rescue them. They are on the west side of
4th Ave between 63rd & 64th Street.