Erole's full name is Erole San Jeust. His first name is likely derived from 'Errol' or 'Erroll', an English male given name synonymous with 'Earl'. 'Erol', a similar Turkish male given name, means 'brave'.
It should be noted that that 'Erole' is the English translation of his name in the English version. The Japanese version is 'Errol'.
'San' is a Spanish word meaning or referring to a saint, such as San Francisco.
I had a bit of fun with Google Translate running 'Jeust' through to see what came up. In Dutch, the similar 'juist' (prounounced something like 'yach-ist' to my ears) means 'correct' or 'exact'. Google also seems to think that I meant to type in the French word 'jeux' (pronounced jhoo or zhu? ((soft z, short u))), which means 'games'.
'Jeust' is a mountain of Schwalm-Eder-Kreis, Hesse, Germany, though I can't determine its meaning. To my understanding, it would be pronounced like 'yoost' (but I prefer the lazy English 'just').
Erole hails from the Wizardry kingdom of Gran, one of the four main kingdoms in the game.
More background information coming soon.
Erole's family isn't mentioned in detail in the game, but his parents are probably nobles. Because of his personality, I have to assume he's an only child, or at the very least he thinks he is.
One of Gran's generals addresses him as "The little devil of the Jeust Family", which leads me to believe he's nothing like his parents (or siblings, if he has any).