Dealing with network congestion

I'm running the Orbi system in a two-floor appartment in a heavily congested building. The bottom-floor only has some relatively onoccupied spectrum available at channel 11. Upstairs it's the opposite and only some space available at channel 6. There are some obstructions which seem to cause my iPhone/iPad with the 2.4 ghz band and cause slow internet issues due to the interference. How can I deal with this? I need the 2.4 channel for some smart home devices so can't turn this off.

Ideally I'd have different channels for each floor or steer the idevices towards the 5GHz band. None of this seem possible, correct?