When you "attract" more hookers than you have available seats for, odd things can occur like the above.
Notice that before actually getting in the car, a hooker may lean down a number of times. Use this time to pull alongside another (or more)...but do not drive too far away from the previous one(s) that are now following you. By driving away as the followers start getting close (and not aloowing any to enter the vehicle), you can build up quite a number of them
If you allow them to start entering the vehicle, they will fill up any empty seats. Any remaining outside will follow you around on foot.
If you then drive to a secluded area and allow the animation to play through, only the last one to enter the vehicle will leave...and the cash on hand will no longer decrease from the stray passengers. You can use this glitch as added protection from being pulled out of the passenger side in a 4-door vehicle, for example (although it's true that the over-the-shoulder camera view glitch is more-effective). In any case, any remaining passengers will otherwise stay in the vehicle for as long as you do.