Is it sufficient for one person living in the house to recite the supplications for entering the home to ensure that Satan does not enter, or is it obligatory for every resident to say them upon their return?

It is from the Sunnah (definition) for a Muslim to regularly recite the prescribed remembrances (adhkar) and supplications (du'a), including the adhkar for entering and exiting. These are recommended acts of worship, not obligatory ones. The remembrance of Allah expels Satan from the home. The recitation by one member of the household is sufficient to ward off Satan upon entry, analogous to the بسم الله (Bismillah) before eating, where the recitation by one person is sufficient to fulfill the core of the Sunnah.