This can be done with relays, but you will need to wire them up safely. A relay is a kind of switch which output closes when an input coil is powered. In this application, two relays with both output going to the lights would work. The input coils would each be wired to their respective devices, and they would never meet in an electrical sense as the relays are separate.
The smart outlet would need to be wired up to the relays, which can be done by plugging in a mains plug with a free ends cable and using the free ends of the cable to connect to the relays.
Please be cautious if you do decide to proceed with such a project. Mains electricity is very dangerous and can easily harm you or start a fire. If you feel you are not experienced enough, please seek professional help.