The "Car Bodyguard" mod adds four additional spaces on each vehicle for your bodyguards to occupy. Pressing insert will spawn up to 7 body guards, pressing delete will kill them one at a time.
Your new body guards will find four news spots on your vehicle to sit on, and they will stand up and shoot at any enemies nearby. Cars, trucks, motorcycles, helicopters, and boats are all supported.
To use this mod, install ScriptHook.
Then copy the files in this zip file into GTAIV's /scripts/ folder.