In English we usually express the subjunctive mood by using one of the modal auxillary verbs can, may, will and shall in their past tenses could, might, would and should.
He should be staying... Most likely
He could be staying...less likely but very possible
He might be staying...even less likely but still possibel
He would be staying...this is really conditional "He would be if..."
Without one of these auxillary verbs the sentence will be interpreted as a definite arrangement.
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