The Council of Saturn

[Infinite]

What indicates to you that they are actually of this octave?

The Council are formed by ascended masters (4D entities who harvested themselves) and Confederation members, as this excerpt shows:

The members of the Council are representatives from the Confederation and from those vibratory levels of your inner planes bearing responsibility for your third density.

(7.9)

In the answer about the harvest, Ra spoke about three levels. Confederation and the Guardians are stated as different levels:

There are those of three levels watching over harvest.

[...]

The second class of those who ward this process are those of the Confederation who have the honor/duty of standing in the small places at the edge of the steps of light/love so that those entities being harvested will not, no matter how confused or unable to make contact with their higher self, stumble and fall away for any reason other than the strength of the light. These Confederation entities catch those who stumble and set them aright so that they may continue into the light.

The third group watching over this process is that group you call the Guardians. This group is from the octave above our own and serves in this manner as light-bringers. These Guardians provide the precise emissions of light/love in exquisitely fastidious disseminations of discrimination so that the precise light/love vibration of each entity may be ascertained.

(51.1)

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I really don't know if there are 7D entities in Confederation. But, Ra used the term "our teachers". I suppose they are from 7D.

I forgot that answer:

Firstly, we do not have complete knowledge of this octave. There are portions of the seventh density which, although described to us by our teachers, remain mysterious.

(81.16)

That confirms the teachers of Ra are from seventh density.