Let's firts start off with the required content. You do not need it if you don't want to use the Delta and the Steve The Bandit NPCs.

Then how to get NPCs in a vehicle with you. You nees to spawn a chair (from the vehicles tab) then you need to weld it to a vehicle. There are also seat entities which are located in "Spawn Menu>Entities>FMod" and there should be two entites, "Seat (Sit)" is pretty much like a chair and "Seat (Stand)" is a seat entity that allows NPCs to stand while in the seat. But keep in mind that the "Seat (Sit)" entity cannot be duplicated, but the "Seat (Stand)" entity can be duplicated.

If anyone asks on anything about the stuff listed here please link this or any other guide or discussion that tells how to do this. Thank you if you read this.