I agree with Bubba's Mom. You can return the car to Hertz(at Portofino) or to Budget (I also seem to remember them having a pickup/drop off for free) and when it comes time for checkout, use a car service with a van to take you all to MCO
Once you are on property at Universal, you will not need the car.....and, this may sound mean - but, checkout at Disney property earlyish, check into HRH and enjoy the pool until the rest of the family arrives. You can use the bathrooms to change and bell services can hold your luggage.