Pohnpei above is correct. I think each of their chosen names also further reflect who they are supposed to represent in the Russian Revolution.
Napoleon (Stalin) is the name of another merciless leader in history.
Squealer (Pravda) is the media mouth. Often sounds that squeal are unpleasant but very real. Also, a squealer is like one who tells on other people. The media is used to "tell-on" what happens to other Russians.
Snowball (Trotsky) reminds me of the snowball effect. The lies spread about Trotsky during early Communism, grew and grew and grew like a snowball.
Just something to think about.
As you say, these are the three main characters among the pigs, who are the leaders of the society.
Napoleon represents Josef Stalin. Snowball represents Leon Trotsky. As far as I know, Squealer does not represent a person. Instead, he is meant to represnt the Communist Party's official newspaper, Pravda.
Stalin was the leader of the Soviet Union after the death of Vladimir Lenin. He was in competition for the top spot with Trotsky. After Stalin won the competition, Trotsky was forced into exile. He was later assassinated in Mexico by Soviet agents.
Squealer represents Vyacheslav Molotov, Stalin's protegee and head of propaganda
Napoleon represents Joseph Stalin
Snowball represents Leon Trotsky
squealer represents the propaganda department