Download the incest patch and open it, there you can see all of the ways characters refer to each other or to mc, and change accordinglyYou can change the way characters refer to you in the game folder - game and then the char{character name}.rpy file
EG. Ruca:
rucafriend - how mc refers to ruca
mcruca - how ruca refers to mc
rucajune - how june refers to ruca (assumably)
rucacharlee - how charlee refers to ruca (assumably)
Edit: the files to change are in the game folder and they are charCHARLEE, charJUNE, charRUCA, charTIFFANY. You can also change the way other characters refer to characters they are connected to, but for incest these are the ones you need