Most insurance companies like to have every household member with a driver's license listed on an insurance policy. Insurance companies usually believe there is a chance household members might drive other household cars from time to time. If you are not going to be driving your nephew's car at all you might be able to be excluded from his policy. It would depend on how his insurance company rates people if his policy would cost more doing this.
If you or your nephew are unhappy with your current insurance policy or company try our site for a Florida car insurance quote on a new policy.