Looking at some example sentences of 占める, it's almost always in the natural form and the particle を is used to describe the direct object, and the particle で the location where something is being occupied, like "彼は会社で重要な地位を占めている".
But in this case, considering the verb is in the passive form, could I still use the particle を here? Would it be always necessary to use で? One thing that I recently learned is that the particle を in transitive verbs in the passive form is often changed to が, as in ～を行う → ～が行われる. Would be possible to use が instead of で here?
I'm not sure but if the author of this sentence wanted to use 占める in the natural form, 店内 should be used as 店内では and 洗濯機や乾燥機 should be used with を, right?