The rights of all parties may be put in issue, tried, and determined by the action. If the court determines a sale of the premises is necessary, the title shall be ascertained to the satisfaction of the court before the judgment of sale can be made. If service of the summons was made by publication, similar proof is required concerning the rights of absent or unknown parties before judgment is rendered. If there are several unknown persons having an interest in the property, their rights may be considered together in the action.