I have my own set of theories on what Trevor, Simon, Juste and Richter did as regular jobs when they were not dealing with Dracula.
Trevor & Simon: More likely they were both mercenaries, the gear that both of them are wearing is not something I would see on a farmer or a huntsman in the 15th and 17th century respectively.
Sidenote #1: I wouldn't be suprised if in the Castlevania timeline the Bohemian War was a retroactive way for the church to cover up the fact that Trevor Belmont was fighting Dracula whereas Simon might have actually fought in the Nine Year's War.
Sidenote #2: This would mean that the events of Simon's Quest occured just a year after the end of the Nine Year's War, Imagine the implications of Simon heading strait back to the battlefield after kicking Dracula's ass the first time only for the War and his wounds from Drac causing him to be in the state he is in CV2: Simon's Quest
(Jeez Fire, way to amplify Simon's badassery so that not only did he kicked Dracula's ass twice but he fricking survived the Nine Year's War)
Juste: I intially though that Juste might have been a merchant of the Hanseatic League, but I recently read the wikipedia article on said league and really the likeliness of Juste making a small fortune working with the league now seems rather slim since the Hanseatic League was going downhill in 1748 due to the fact that the world was changing around it and the League couldn't keep up with the changes. However the league did persist till 1862, so it might still be possible for Juste to be a somewhat successful league merchant.
Richter: He might have been a merchant as well, although an independent one. The way Richter and Juste both dress practically screams 18th century merchant to me since the nobility weren't the only ones wearing Justacorps like Juste's and Richter's. Infact I would say that both of them were well off enough to be able to afford the clothes they wear but otherwise still did work, I notice that most of you guys prefer to go with the "Belmonts as nobility" angle, Instead I prefer to see the Belmonts as common down to earth people like you and me. Heroes who work to make a decent living, but sometimes tend to get lucky.