Hi,
I have a few ideas you might wanna consider. Obviously a lot of people are into anal, oral, ass-to-mouth and food play, so with this in mind...why not make a scene, or even a whole movie dedicated to this but in a more intimate way?
The scene could include 2 girls and 1 guy and put on a bit of close up perspective so that you really can see what is going on. This would make it more emotionally intense which I believe will attract a lot more viewers.
Girl 1 characteristics: Very sweet and young/fresh looking, beautiful face, slim, happy, eager, giggly. You got plenty of those
Girl 2 characteristics: Milf or 'babe' type, sexy, well developed plump body, calm, mature, thin waist with broad hips, nice plump ass, save some pubic hair but well trimmed. Possibly big tits but the lower part is of most importance as it gets most attention.
The Guy characteristics: Well, basically the biggest dick you have available
Now to the sex...
Foreplay: Some kinky seduction, roleplaying or the like. (Incest themes are really kinky)
Position 1: Older girl/woman positioned doggy style with her awesome ass up in the air. The younger girl lies on her back with her chin between her partner's plump ass cheeks just happily waiting to make the cleaning job. Very up close camera work. The guy rams the ass slow or fast pulling out to get his dick cleaned off by the pretty girl. (you can apply all sorts of messy stuff here, like cream, chocolate, marshmallows goo, and more).
As I described above, penetration will be either slow or intense but very deep, shifting between the ass and the pretty mouth (or throat).
Position 2: Girls doing 69 with the slim girl on top. The guy ass-fuck Girl 2 while Girl 1 is eating pussy. Also here Girl 1 will have the opportunity to clean the cock. (Pee or squirting orgasm from Girl 2 can be included at this point.)
Position 3: Girl 2 on all four. The guy stands behind and shove things(food stuffs) up her ass and pokes them in deeper with his cock. Girl 1 is standing on her knees waiting for the guy to step aside and force her beautiful face in between the ass cheeks and let Girl 2 do her business.
Position 4: Girl 2 is sitting on the face of Girl 1 and shit in her face or mouth. During this process Girl 1 is masturbating heavily.
Position 5: Very dedicated and intimate piss drinking! Girl 2 sitting or laying back with legs spread far apart while Girl 1 is gulping.
There are more, but lets start with these.
If you can get the actors motivated and dedicated to do this you will have a winning concept that will make the rest of the porn industry look like fucking kindergarten.
Cheers