I think that there were three Emperor Napoleons, andf yes they were related. Various other relatives were placed on the thrones of other European countries, as well as France.
There were two Emperor Napoleons, Napoleon Bonaparte and Napoleon III. Napoleon II was the original Napoleon's heir (his son), but like Louis XVII he never reigned. Louis Napoleon Bonaparte, or Napoleon III, was the original Bonaparte's nephew and took/seized power after the abdication of Louis Philipe in 1848 (he was elected President and then altered the Constitution to make himself Emperor - a bit like Hitler did in Germany a century later).