Section 7. Upon such petition the court shall cause not less than seven days’ notice of the time and place appointed for the hearing to be given to the alleged mentally ill or mentally retarded person, to the department of mental retardation in the case of a petition filed pursuant to section six A and, if the alleged mentally ill or mentally retarded person is entitled to any benefit, estate or income paid or payable by or through the United States veterans’ bureau or its successor, to said bureau or its successor, except that the court may, for cause shown, direct that a shorter notice be given. No appointment shall be made without such notice to the heirs apparent or presumptive of the alleged mentally ill or mentally retarded person, including the husband or wife, if any, as the court may order. In the matter of said petition and all subsequent proceedings relating thereto said bureau or its successor shall be deemed to be a party in interest if the alleged mentally ill or mentally retarded person is so entitled.