How to Solder TQFN packages that are on both sides of the PCB
There are a few ways to do this:

1) Direct the heat flow on the PCB

There are a few ways to direct the heat flow, you'll have to get creative especially if the parts are near each other. You could put a heatsink on the components that you don't want to move around, or cool it down with a cool air flow on the bottom side (which might make soldering on the top side harder. It might be advantageous to keep the flow of heat in mind if you ever rev your board. 

Another clever way to direct heat is using aluminum foil around SMT parts to keep the hot air away from other components and the board. The picture below is an example (although they are using an iron, but this also works for hot air)

 

2) Use solder with different melting points

The way two sided PCB's are manufactured are with solder with two different melting points, a higher melting point for the bottom side of the board (which you assemble first) and a lower one for the top side. Not a great option for prototyping