IESP-348 is one of my favorite movies. You might like it, if you don't mind your incest to come with r***.
In the first part grandpa, father and two sons have their way with mother and daughter (in seperate rooms), in the middle part an uncle and two nephews show up to have sex with the two and the last part goes back to the original group and this time mother and daughter are r***ing next to each other.
The cover even has a family tree thing to show how they're related and who has sex with who.
I love this series. I think the third is my favorite.
Just so happens I've been figuring out how to use Google's APIs for transcribing+translating English language subtitle files (see this post) and I've done the items of series I happen to posses (1-7, if there are more I haven't looked).