I don't know of a way to do what you are asking, but I can tell you that there are easier ways to blur faces. I am away from my editing PC right now, so I can only give you the general idea. You could use track mattes, or use garbage mattes. Of the two, I think that garbage mattes might be the easier, depending on the content of the video.
Try this little experiment and see if it helps.:
Put your original clip on track one and a second clip on track two and a third on track three. Blur the clips on track two and three. You will need to temporarily poke out the eyeball on track three to see what you are doing on track two. Apply the 8 point garbage matte to the clip on track two and animate it to cover the face of the first person.Enable track three again (put the eyeball back) and apply the 8 point garbage natter to track three. Then cover the second face.
If you prefer track mattes, just make a white oval in the titler and use it as a track matte for the first face. Then make a new title based on the first and use it for the second face. That means you have to put the video on tracks 1, 2 and 4 with the mattes on 3 and 5.
I can't picture how you are using an adjustment layer so I can't help with that. But give the mattes a try. If you can't get 8 points to make a decent enough matte, use the 16 point garbage matte instead.
how do I have two adjustment layers, each one independant from each other and only affecting the original footage?
Make sure the layers do not overlap. Any layer will affect everything underneath it, that's just the way they work.
I've been playing about with your suggestion all day and it is a much better way of doing things. I settled on track matte and made an oval in the titler like you said, repeated for the second face and it's a great result. I tried the 8 and 4 point garbage matte but the footage is too jumpy and out of focus at times to keep moving the points around in order to cover the faces.
The two faces are always in the scene so there has to be overlap, thus it won't work doing it with 2 blurred adjustment layers in Premiere. I had been doing it like this in AE with 2 blurred and animated adjustment layers fine but AE didn't give very convenient manipulation of the audio track. Using Steven's suggestions is working well for me now.
That is why it is always nice to have more than one way to do things. When the image distorts a garbage matte can be handy, but if an oval is good, you can just change the scale to deal with changes.
I am glad it is working out for you, and thanks for reporting back. It helps to have feedback so that we can improve the way we answer questions.