Somebody wired your breaker box wrong? What is the main in your breaker box?
Too much load on one side
It is most likey wired with all your loads on one side including one air
And the other side is only carrying the other air
Yes it could be reconnected for 230v but you don't need too do that
Just need to have a two line input breaker box, using both generator output lines
And balance the load distribution
The other question is the water heater on LP? What about the fridge?
When In hot weather using the genset and air, making sure those stay on LP manually is a good idea, so they don't switch over and use the Onan power
That Onan is big enough provided the loads are balanced