Blowing a multichamber ocarina
Most of the technique used to blow multichambered ocarinas is the same as single chambers. If you have not already I strongly advise reading 'How to blow an ocarina correctly'. The main difference is that each chamber has its own windway and voicing, thus you have to constrain your air to a single windway.
Constraining the air to a single windway is done by forming an aperture with the lips. This aperture should be moderately sized as it will create a noisy tone if too restricted.
LIGHTLY touch the mouthpiece of the ocarina against the aperture, in line with the desired windway, using just enough pressure to create a seal. You should have as little of the mouthpiece in your mouth as possible. Positioning it too deep in your mouth creates excessive friction which makes it difficult to switch windways, called chamber switching.
You may find that you are blowing into two windways at once. If this happens, you need to vary the width of your lip aperture. It is possible to finely control the position of your lips to do that. However, I don't know how to explain it. Doing so came naturally to me having previously played the flute. Experiment with blowing through your lips and varying the shape of them.
Usually, you will only be blowing one chamber at a time. The nature of the breath curve means that they normally don't sound in tune if played together. As when playing a single chamber, you should angle the ocarina so you are blowing directly down the windway. Tilting it sharply up or down kinks the air passage and results in a noisy tone.