I think
RapeLay would fit the bill.
It's been a gazillion years since i've played but as far as i recall, it has blackmail, rape and incest (2 sisters+mom). Not exactly "hard" to bang, but im pretty sure you need to meet requirements when doing the girls in order to subdue them (again, counting on memory here). Different ways for different girls. And depending on how hard a bargain you drive, you can get a "bad" ending (involving Mr. Knife).