I know this is late and probably more than you want to know about US insurance, but I'm not as confident as the other commenter that the stepdad would be a covered driver. Insurance in the US is generally not restricted to named drivers, but things can get wonky if you live together. A lot of insurance policies won't cover people you live with if they're not named, because it's a fairly common way to try to pay less for coverage while still letting someone else use the car frequently (think like a parent leaving their teen driver off the policy since teen drivers are more expensive).

I honestly don't know how this would work with a part-time stepparent situation, and it may vary depending on your state since insurance laws are generally set at a state level, but I'd definitely want to talk to my insurance company to make sure he was covered if he was going to be driving the car regularly. I wouldn't assume he would be covered.