The spouse of any decedent dying domiciled in the Commonwealth, and if there be no spouse, or if he has forfeited his rights, then such children as are members of the same household as the decedent, and in the event there are no such children, then the parent or parents of the decedent who are members of the same household as the decedent, may retain or claim as an exemption either real or personal property, or both, not theretofore sold by the personal representative, to the value of $3,500: Provided, That property specifically devised or bequeathed by the decedent, or otherwise specifically disposed of by him, may not be so retained or claimed if other assets are available for the exemption. The surviving husband or wife shall be a competent witness as to all matters pertinent to the issue of forfeiture of the right to exemption.