Simply ring your Insurers, explain your family live locally etc and they will probably be happy to cover it (They sometimes raise a charge or restrict cover). They may have some requirements such as switch off mains supplies and drain tanks down.
Its best for your family to get a small note pad and make a note of the date and time they visit, any damage and any actions they take. The Insurers will normally want to see proof of when they visited and this will act as proof