Section 31. A complaint may include two or more contiguous parcels of land, or two or more parcels which constitute one holding under one and the same title, within the same registry district. But two or more persons, who claim in the same parcels different interests which collectively make up the legal estate in fee simple in each parcel, shall not join in one complaint for more than one parcel unless their interests are alike in each and every parcel. The court may at any time order a complaint to be amended by striking out one or more of the parcels, or by a severance of the complaint.