Could someone be charged with "solicitation of prostitution" if they were...?

I would imagine both charged, and found guilty.

It is unlikely that a judge or a jury would buy that excuse.

Presumably the driver did NOT have a gun at his head to prevent him driving on, and saying to the passenger "Not in my car, you don't !"

Put yourself in the shoes of a judge or jury member and consider whether you would believe such a fairy tale.

Having said that ... you might try thr defence of saying "The passenger threatened to tell my wife / girlfriend that he knew about an affair I had with his sister or whoever if I didn't stop.

I would find you not guilty on that defence.... you could also use that response to your wife .... maybe using an alternative blackmail reason.

The elements of solicitation require an act that means the driver must have participated in some way. Just being in the car would not have done it.

I think they will be unless theres evidence proving they tried to stop it from taking place or if the driver was ignorant to the situation (poss talking in code or street jargon)

It's very likely the charges could be dropped against the person that didn't participate. However, they might not be just due to the fact he was with them. If it was the driver that didn't participate, then charges will stand because be knowingly drove to the location. Hope this helps.

charged and found Guilty

have you never heard of a threesome?

and yes hookers will do 2 guys or a whole damn truckload

what do you think happens at Stag parties?

ONLY THE PERSON OF SOLICITED THE HOOKER WOULD BE CHARGED.