Hi I would like to request a mod that makes romantic interactions between family members (other mod allows it) hard. So even if they do have high relationship it still hard to develop incestuous romance. However once romance is established there is no penalty when romantically interacting with one another.
Additional option would be that other family members and friends of either party will hate seeing incestuous romantic interactions (unless they have one themselves). Strangers are fine with it as they dont know the couple.