The rating of a charger or charging port indicates the maximum output it can provide. A device connected to it will only draw as much power as it needs so you don't have to worry about the port delivering excess power. On the contrary, it's better to have a charger with an output rating at least equal to if not higher than the requirement of the device you're plugging into it to ensure that it will charge properly.
I don't think you can combine those ports together (if that's what you're suggesting) and I wouldn't do that, just connect each device to a single port.
Fast charging as stated is 9V instead of the usual 5V for standard USB charging, I doubt that any built-in car ports are capable of this and will most probably deliver only 5V.
Also note that all the power ports in a vehicle are most likely on the same circuit (this can be checked by looking at the fuse box diagrams in the owners manual), so the total draw of all devices plugged into the ports at any one time should not exceed the current rating of that circuit.