Hello Chad Labarre,
I don't know Charles Brehm, Jean Hill, or Marie Muchmore well enough to be able to judge whether they might have been willing to help in this horrific act.
In the case of Charles Brehm, this would be particularly severe, as he expected his 5-year-old son Joey to witness the cruel act with his own eyes. I definitely do not rate Charles Brehm as radical, especially since he, like Hill and Moorman, looked very upset and traumatized after the crime. With the best will in the world, I can't imagine it was acted (although my impressions don't really invalidate your scenario either). It should also be borne in mind that the more people are involved in an act of this magnitude, the risk of non-secrecy increases immensely.
On their point that the second babushka was in a car and exchanged the first BL shortly after the assassination:
If I'm not mistaken (I often have problems assigning a point in time to the pictures), the fourth Wilma Bond photo should roughly correspond to the point in time when a policeman (I think Hargis) in the Bell film runs up to Babushka Lady ("BL 1").
Bond 4 also features one or even two people with cameras filming the Newman family (Doris Mumford lying next to them, I believe), which I suspect is Dave Wiegman and maybe Thomas Atkins (as I said I'm very unsure about that, on Bell they are not visible, maybe outof view area ?). But that would mean that Camera Car 1 must have already passed the babushka lady.
We should see "BL 2" on the Nix-Film, because the bag strap can be seen quite well here.
But that should also mean that "BL 2" can also be seen in the couch film (camera car 3). This results in a very short period of time because, according to the Sixth Floor Museum Dallas, the scene with the Babushka Lady in the Nix film was probably recorded a little more than 30 seconds after the fatal shot. On couch you see "BL 2" a little earlier. Couldn't see a car on the couch, which would have allowed the "BL 2" to get out beforehand, which makes the time span quite short. So far, I have not been able to find a car on various photos that would have made this possible for the BL 2 (possible photos here might be of Phil Willis or Jim Towner).
I also don't assume that a car would have squeezed in during the motorcade. Therefore I am still convinced that there was only one Babushka Lady.
Some are of the opinion that the Babushka Lady was very much involved in the assassination, not as a shooter, but as a kind of signal generator, since a light source appears on the Zapruder film (interestingly only in the qualitatively improved versions). I have no idea whether this is really true.
My arguments are certainly not the most well-founded either, but they reflect my previous impressions and views.
Many greetings