I've tried what Daiz recommended in http://www.scirra.com/forum/ignoring-collision-from-one-layer-to-another_topic40099.html#p51640 and that kind of got the lane shifting mechanic working except that it seems to apply globally to anything with a platformer behaviour (if any other players are around, they'll probably shift lanes too).
Is it possible to have an object ignore families or other objects with a specific attribute? That's the only way I can see this working right so that the players can shift lanes and if there's any enemies on lane 2 and the player is on Lane 1, neither one will be able to affect the other.
If there's a better way to achieve what I'm trying to do, I'm all ears too. I'm pretty new to Construct and I'm open to learning how to use it better.