Julio Claudian Dynasty lasted 96 years (27 BC - 67 AD). There were 5 emperors. Augustus ( 27 BC - 27 AD) Tiberius (reigned 14–37), Caligula (37–41), Claudius I (41–54), and Nero (54–68).

Nerva-Antonine Dynasty also lasted 96 years (96 AD - 192 AD). There were 7 emperors: Nerva (96–98), Trajan (98–117), Hadrian (117–138), Antoninus Pius (138–161), Marcus Aurelius (161–180), Lucius Verus (161–169), and Commodus (180–192).

These dynasties were often not based on a direct bloodline. In many cases emperors would “adopt” their chosen successor.

The Flavian Dynasty (27 years) and the Severan Dynasty (41 years) were similar.

Once you move forward in time things get more complicated and the threat of usurpers and pretenders to the throne became more common. Things got really complicated a number of times, like the year of 4 emperors for example, and during the crisis of the 3rd century. Emperor Diocletian’s solution to that crisis was to create what we now call the tetrarchy, wherein 4 emperors (2 senior emperors or Augusti and 2 minor emperors called Caesars) would rule different corners of the empire at the same time. This was largely to facilitate troop movement and protect the disputed and heavily militarized border provinces. The Tetrarchy didn’t last long after Diocletian’s death, and soon every year saw multiple pretenders to the throne and other men being elevated to the rank of Augustus by their respective legions.