Yet another 3-way smart switch question
Normal use of neutrals/ground.
Line @ front door, re-task red to traveler.
Red as traveler in downstairs 1-gang. Tie both blacks together as &quot;load&quot; from main box.
Red as traveler in upstairs 2-gang. Tie both blacks together as &quot;load&quot; from main box.

Shout out to @hHarper - Reinstate Monica and @ThreePhaseEel for the assistance.