In general, all rental companies charge for the 2nd driver or spouse. As the renter, you receive no additional benefit from this fee. If you have another car with insurance, it's very likely that...
If your 18 year old has a license and NOT a permit, then you can probably rent a car.But I pretty sure you can not use a permit, you need to have a license.
My recent rental with enterprise for the week of rental if your paying cash- the deposit was 100.00.Refundalbe upon car rental return on time with out any damage.