Well... this one is short!

Never happened to you that you were making a mission and then you add an actor as a passenger and another as a driver and the passenger doesn't reach the car and the driver drives off the scene, leaving the passenger running?, xDDDDDD

Well... there are two ways to prevent that:

1)
You can spawn the driver actor after you spawn the passenger

2)
You can spawn the driver further from the car than the distance of the passenger between the car. So the passenger will get in the car quicker than the driver