First you use two phrases "can be constructed out of" and "complete generating set". I think I understand what you mean here but it is possible there is a misunderstanding.
I was hoping you might get a better answer as the following is really a strategy and not a complete proof.
Take the category generated by your tensors (I hope we are in agreement as to what that means). Then this is a rigid symmetric category. In fact it is what Deligne calls a tannakian category together with a fibre functor. Then Tannakian reconstruction reconstructs an affine group scheme which has this category as its representation category (I think in the physics literature they would refer to Doplicher-Roberts).
There is a discussion of reconstruction at
Tannakian FormalismTannakian Formalism
Then if this is not $F_4$, what is it?
P.S. Do you need the volume form? I have not seen this in this context.