They have a dizzying variety of needs, and meeting them depends on the professionalism of those who do the caring — the army of case managers, clinicians, social workers, nurses, doctors, counselors, therapists, and fundraisers who spend their days keeping chaos at bay.A pair of new projects, 90 Sands in Dumbo and El Borinquen in the Bronx, makes it clear how crucial it is, when you get your first latchkey in many years (or ever), that it open a door onto a space that’s private, sunlit, safe, and serene.Sandwiched between the Brooklyn Bridge and Manhattan Bridge ramps in one of the city’s most expensive wedges of real estate, 90 Sands is a big, ungainly slab built in 1992 to house 1,000 Jehovah’s Witnesses, whose meals issued forth from an enormous basement kitchen.Staff can coax (but not require) them into taking advantage of the available services; the design needs to draw them into the unfamiliar experience of feeling at home.“These are beautiful buildings, and that’s intentional,” says Pascale Leon, the executive director of the umbrella organization Supportive Housing Network of New York."