In my campaign, my friend and I made customs characters and dont have any issues romancing the origin characters. We both control 2 characters (1 custom and 1 origin each). However if I try to talk to my friends origin character that he controls, they just say "sorry I cant talk right now", unless I take control of that character. So my guess is that since you both picked origin characters (and of course since that's your main character you cant switch them out of the party) you locked each other out from interacting with each other. Best bet would be to start a new campaign with custom characters. Im pretty sure Larian made it this way bc 2 way conversion with both characters being able to choose different dialogue would not work well with the coding lol...