Unit 3 was just behind a wall, but 1 and 2 were quite far away (300-500m).
They all had multiple serious incidents before and after the Chernobyl Disaster (1982 - partial core meltdown at #1, 1984 - incidents at #3 and #4, 1991 - fire at the turbine hall of #2). This was the most unsafe nuclear power plant in the whole USSR and the operators were in grave danger all the time.