would just kind if sit there
I wouldn't worry about that, especially when they advertise that they do duos together. i.e. they are professionals at this service.
I think that you will have something on your mouth (kiss, nipple, pussy), while the other attends to your cock (with hand, mouth, pussy). All that while your hands roam freely. There will be plenty for each of them to do simultaneously.
To me it's sensory overload. But the idea of pumping one spread-legged beauty while dfk'in the other...does give me pause.