The writ in the action of ejectment shall not abate because all the tenants are not sued, but those on whom service is made shall answer for such part of the premises only as they set forth in their answer, and disclaim as to the remainder. If a defendant disclaims as to the whole, he or she shall recover his or her costs, unless the plaintiff proves such defendant in possession of all or part of the premises demanded at the commencement of the action.