Most places will not consider a room without a window or built in closet a bedroom. The window is a fire safety thing. The closet thing - idk, I guess it prevents people from trying to section off rooms or stick kids in a laundry room or hallway. I get that, but it is flawed since lots of older houses do not have built in closets in what’s clearly supposed to be a bedroom.

Even when selling a house, you can’t call a room a bedroom if it doesn’t have a closet. You have to call it a “bonus room” or home office.

Either way - unless both bedrooms didn’t have a closet, why wouldn’t your friend just give the kids the room the with the closet?