I actually roleplayed a character back on WoW who dated and eventually married her older brother who had completely changed his identity over the years due to being a rogue who took very dangerous jobs and required him to do such.Â
What me and my RP partner usually did was that we kept that they were siblings under wraps until we got to know the people we were roleplaying with. Some people are accepting and willing to go along with taboo themes, but some people are not. You need to be sensitive of the people who are not. So yeah I wouldn't spring the whole incest backstory thing on them right away, take some time roleplaying with them first.Â
It also doesn't hurt to ask and discuss things about your character's backstory OOCly. See what they're okay with and not okay with. And if they're not okay with it I'm sure they'll respectfully let you know.
What me and my RP partner usually did was that we kept that they were siblings under wraps until we got to know the people we were roleplaying with. Some people are accepting and willing to go along with taboo themes, but some people are not. You need to be sensitive of the people who are not. So yeah I wouldn't spring the whole incest backstory thing on them right away, take some time roleplaying with them first.Â
It also doesn't hurt to ask and discuss things about your character's backstory OOCly. See what they're okay with and not okay with. And if they're not okay with it I'm sure they'll respectfully let you know.