This is a building built in ~1863 with four 3-room flats on each floor; it was occupied until 1935 when it was abandoned because it couldn't comply to new housing laws. The museum project started in 1988 when the building was purchased. They have done extensive research, finding many artifacts and identifying ~1300 of the former tenants or workers who occupied the building. The tour guide explained the evolution of the building with the addition of such amenities as gas lighting and cold running water.
Many of these apartment housed a family and were also used as mini-garment factories so these tiny apartments had many people in them. They have several apartments set up as they had been so you get a pretty good idea of the layout and with our tour group of about 15 people you get a bit of a sense of how crowded they were when they were occupied. I suspect that there are plenty of currently occupied by current-day immigrant buildings that aren't too different from these except they aren't museums but reality.
In one of the rooms they had some printouts of resident names. When leafing through them I found a Lustgarten family. Now, my father's mother was named Dora Lustgarten and lived in the lower east side and died in ~1908; none of these Lustgartens were named Dora but perhaps they were relatives. His father and grandfather was in the garment business - I think they made men's suits and overcoats. I don't think they were workers, and I certainly hope he wasn't an exploitive boss. Sadly with no known living relatives I can't easily followup on my family history.