While the majority of courtiers at the court of Arx can claim noble blood and count themselves as peers of the realm, the guild of courtiers places no such restrictions of birth upon the men and women they train to attend to the highest nobles. As experts of handling the social nuances of Arx, the courtiers of Arx are famous throughout all of Arvum for peerless grace, effortless charm, and precisely perfect courtesy- at least taking great pains to be sure that the courtiers that accompany high nobles to social functions meet their exacting standards to uphold the guild's reputation. Successful courtiers can serve as trusted messengers, talented diplomats, prized entertainers, and the favorite companions for the most powerful political figures in the city. Some of common birth can find themselves ennobled by successfully maneuvering the treacherous waters of the court, but even those who do not earn that distinction are usually afforded the same courtesy reserved for nobles.
Please note that there is nothing explicitly or implicitly sexual about their work at all. The word 'courtier' could be substituted with 'envoy', 'attache', 'aide', 'diplomat', 'party planner', 'maitre d', 'concierge' and similar, so if the context of a sentence wouldn't fit replacing the word 'courtier' with one of those, it probably doesn't work thematically. Arx as a game does not and will not support PCs that are prostitutes, Thralls, or any other PC who lacks personal agency by design.
In regards to the courtiers of Whisper House, it is expected for full members to maintain impartiality, and this typically means they don't marry into any family, nor can they have noble title. Commoners, including illegitimate children of nobles, even as members of houses are not typically seen as having significant conflicts with duties of Whispers until and unless they would take overt actions that would conflict with their duty as a Whisper and have to choose.
Examples of this would be if say, a noble bastard acting as a Whisper specifically undermined another house in diplomatic negotiations to the house of their parentage's benefit in a way that became publicly known, and other houses complained about Whisper impartiality. But commoners just having blood ties to a house is not, in itself, considered enough of a conflict, though Whispers remaining unmarried is a traditional sop to avoiding conflicts of interest. If that same Whisper for some reason were ever ennobled, it would be expected they leave the Whisper House and remain in the organization as a Non-Whisper Courtier.
As for engaging in personal conflicts outside of Whisper House, the Whispers don't relish the drama, but they can get away with more due to not being a noble house. They can say, 'someone was not acting as a Whisper' and have it pass by unchallenged by quite a bit of the populace, which a noble just can't do. Being an occupation rather than a birthright helps. As long as the Whisper House remains publicly neutral in such instances and don't have to get involved in arbitration, they are pretty much fine with their members pursuing their own causes and would rightly scoff and dismiss anyone claiming they need to act: ie "We only take part in disputes among or involving the peerage when requested and paid to, as is traditional."