EXACTLY. In the book the Volturi were seriously outnumbered (thanks to the wolves) and supernaturally powerless (thanks to Bella). Unlike (what seems like) the BD2 trailer, in the book the Volturi did not depend on their witnesses fighting with them. Although, we know they were willing. But in the book, I think the numbers are even worse for the Volturi than you figured. I’ll explain in a moment.
Regarding Jane & Alec: I was referring to the Cullen side POV, you know, when Kate and Vladimir say something like they would give Jane and Alec the beat-down and destroy them. Also, I had forgotten about Renata. You’re right, she would not be one of the ones fighting.
Come to think of it, now that you mention the Volturi’s POV, if we look at things from Aro’s POV he would not have had any of the guard members with special abilities fighting knowing what Bella was capable of. He would not want to risk losing his prized possessions or treasured pieces. Consequently, there would be 11 Volturi individuals not fighting (not counting the wives): Aro, Marcus, Caius, Jane, Alec, Renata, Chelsea & Afton (they’re a packaged deal and without Chelsea what would keep the supernatural strong bond in the guard and coven), Corin (I personally think she is as, if not more, important than Chelsea, she keeps Marcus and the wives content AND she keeps Chelsea content or addicted to the Volturi too), Heidi (she’s the one who makes dinner deliveries, although someone else could do the job, but not as good as Heidi) and finally Demetri. I think they would not want to lose Demetri being he is the world’s best tracker and now that the Volturi know they are outnumbered and powerless to Bella/Cullens Allies I would think they might give the rejected applicants another look.
In conclusion, this is how I figure the numbers (please correct me if I’m wrong). Book Battle Field scene
Cullen Allies: 27 fighting Vampires + 16 fighting wolves = 43 Total
Volturi Side: 18 fighting Vampires and zero fighting witnesses = 18 Total
Hence 18 v. 43
nightmare for Volturi (they really came unprepared).Presumably, though not confirmed, BD2 Battle Field scene/trailer
Cullen Allies: 24 fighting Vampires + 17 fighting wolves = 41 Total
Not counting Alice, Jasper & Kachiri because I didn’t see them in the trailer.
Volturi Side: 70 (we see in trailer) – 13 (Volturi coven & 8 guard members) = 57 total
I’m not sure about the number 13 but I counted around 10 at the battle field’s fire, so 57 roughly give or take 2 or 3.
Hence 57 v. 41
= hard work in store for the Cullen side, especially if Bella is fighting (as we see in the trailer) and not concentrating on shielding the right people. Although, Zafrina could blind multiple people at the same time so there’s still hope in this scenario. Benjamin has pretty cool tricks too. But they are cutting it dangerously close.
Lastly, Unaccounted BD2 Variables that we know of: French coven, Alice, Jasper and Kachiri. Also, I didn’t think they would have Jacob and Renesmee running away and possibly fighting so maybe Huilen and Nahuel would be fighting and/or running too. Also, I’m probably missing a whole bunch of other unaccounted variables that I should be noticing plus all the unaccounted variables that are in the movie we don't know of but these are my figures as I see them now.
Please feel free to correct me if I’m wrong. It’s late and I’m tired so I’m sure I messed up somewhere.