Its been a long time since i have had roommates, but i do have a spouse, and know people with driving age kids.

Your insurance company is within their right to say "these people have regular access to your car, they either need their own policy, or be under yours" Usually this comes up only with young or new drivers, or as i mentioned above, you are in your 20s living with rando roommates on a cheap policy.

There SHOULD be an option to have a rider that explicitly excludes them from coverage. The gotcha with that is, if you want to let them borrow your car for a day, you are now not covered, and also committed a crime, if something happened, unless you want to charge them with stealing your car. That could be as simple as they were doing you a favor and moving it from one side of the street to the other, and hit something.

I'm going to assume if everyone isn't really young, something one of the parties involved did was big enough to flag you with your insurance company on an address search, in which case, you should be very cautious about loaning them your car. Likewise if they got flagged in an address search, well, someone is using your address.

Edit: just re-read your post, and the reason you PROBABLY got flagged was your BF's parents own the home so came up in an address search. So don't want to accuse anyone of anything. You SHOULD be able to tell your insurance company they have their own policies, and be good to go (they may want proof). Again, i'm going to guess you are under a cheap policy that takes no chances, or are new to the insurance company or a new driver.

If your company still won't take that, i'd start shopping around, but ultimately its up to your insurance company if they want to insure you (outside some protected stuff) and are free to refuse your business.

TLDR; someone probably has something bad on their abstract.