SECTION 5. Defendants, persons who may be; costs

A person claiming an estate or interest in the land, although not named in the complaint nor served with process, may appear and answer thereto; but a defendant not named shall not recover costs against the commonwealth, unless it appears that he has an estate or interest in the land, although the commonwealth fails to establish its claim thereto. If there are several defendants, the court may award costs for or against any one, as if he were the sole defendant.