It is possible there is an issue with multiple Syphon Servers in the jSyphon library (which Syphon for Processing leverages). I admit I have not tried this. Are you sure each PGraphicsOpenGL “G” is unique and each .getTexture call is properly returning a unique, populated GLuint textureID?
Can you make a simple simple test case, and post a bug on the google code bug tracker? Thank you!