Gordie - this is going to sound a bit cynical but perhaps I am. It seems that you've got some great IRL support happening to which is fabulous.
I would suggest that while not obviously agreeing with her fantasy of "we'll all be friends" to not pop that bubble right now.
We've all seen stories about how they can flip from marvelous to monster in a heartbeat.
Get the deal done and get the best one you can for yourself and your kids. It may seem less than honest but let her live with the fairies for now. Truth darts can wait until after that document is signed. Negotiating with the Princess of Fairy Land is much easier than the Monster from the Black Lagoon. Just make sure that you protect yourself, your children and your future. If she's willing to agree to termination clauses on re-marriage or even co-habitation, take them and be grateful. I negotiated a lower separation amount for a fixed period but without termination clauses.
Also - expect her world to fall apart and that you will need to be there for the kids. It might not. We don't know. But your kids need to be kept safe.
It's not very "DB" but the attitude that helped me was to not focus on what was "fair" but rather on what it would take to get a deal done that I could swallow. Also try to think about how the deal can be pitched so that it looks positive to her. Don't have anything that looks punitive.
Stay strong. You can do this.
On BD H52, W50 T27, M26 S21, D23 BD-9-Mar-16 D-15-Jan-18 Final-19-Apr-18 I am a storyteller. The story may do you no good. But a story is never for the listener. It is always for the one who tells