Two people can't insure the same car in Ohio. In that state, the insurance follows the vehicle not the driver so there isn't any reason to doubly insure it.
To insure a car in Ohio you need to be one of the owners on the title. You can't insure something that you don't own. The insurance policy covers anybody driving it so if you loan your car to a friend you are also loaning your car insurance. If the person lives with you or has regular access to the car, though, you need to add them as a driver.
It's for these reasons that it wouldn't make any sense for there to be multiple insurance policies on just one vehicle. In the event there was a claim, such as a car accident, and there were two policies just one of the policies would cover it. No two insurance companies are each going to pay out for the same damages on a vehicle. To try to have something like the car being stolen covered double by two insurance companies would constitute fraud.