Utility companies neither know nor care about who owns a property. They simply provide a service to the people living there, irrespective of whether they're the owners, tenants or anything else. If your parents are continuing to live in the house, there's no reason to contact the utility companies
Your parent's contents insurance should remain unaffected by the change in legal ownership of the property but the insurers covering the buildings policy will expect any claim to come from the owners of the property (and to pay their cheque to those owners). Since your parents are no longer the legal owners of the house, any policy they hold may be invalidated. So you should definitely contact the insurers.
Chris