Car insurance?

Hi! I’m trying to help my dad find car insurance which allows for other drivers to drive his vehicle. I’m going to be visiting and he wants me to be able to drive his car while I’m there so I don’t have to rent. He says his current insurance won’t permit that, but others do, and he can’t seem to find anyone to switch to. A couple of questions:

Are there carry insurance providers that allow this? Is it hard to switch insurance providers?