I'm guessing here that the shuttle thingy is a bike carrier, on which you hang bikes by the top tube.
And that your issue is that you have full-suspension MTBs, whose funky frame geometries aren't compatible with such a carrier?
Well, I've seen a gadget called something like "top tube adapter" or maybe "cross tube" or "cross brace".
Anyhow, it was a bar that clipped on between steerer tube and seat post, creating a top tube that could be hung on a bike carrier.
A regular, diamond frame (HT ) MTB will do just fine on a bike carrier.