My mate suggested a voltage divider.
Don't listen to him he is so wrong.
What I thought might work is using the 9V power supply to regulate to 5V and 3.3V in parallel, but I can't seem to work it
If you want to generate these two voltage rails from a single source then you will need two regulators. You can wire them up so they both take their inputs from the 9V or you can feed the input of the 3V3 regulator from the output of the 5V one.