Instabul, I think you have those rose coloured glasses on again. Some of us Bio Mom's resent the new and improved Stepmom's trying to filling our shoes and running interference or having Dad doing it for them to make them happy. Although I am fairly new here too, I have yet to see threads where Mom is gushing over Step-Mom. Its almost always, Step-Mom bashing Bio Mom. Correct me if I am wrong members.
What you can do for your Fiance, besides respecting her beliefs, is too settle your dispute with your ex, and if you have to speed it up, settle before this ends up in court. You dont have time on your side waiting for the court system and keeping your upcoming marriage on track. IMO the ball is in your court. I do feel for your Fiance walking into this can of worms. I wish you all the peace and happiness, but I think your setting your Fiance up for a rough ride.
You might be right Kate; none of us as have crystal ball. That said, I agree, for sure Bio Mom will not be gushing over Step Mom

. However given the personality of future Step Mom, her bashing Bio Mom is highly unlikely. Also without going into stereotypes, keep in mind cultural differences at play here. That would be an entirely separate conversation, although an interesting one.
Step Mom might question in private with me why Bio Mom does what she does, and Step Mom might not understand why Bio Mom does what she does. But in terms of bashing it's far more Bio Dad bashing Bio Mom in private with Step Mom listening to my rants. I try to limit those episodes because who wants to listen to their spouse vent about their ex too often?
Regarding settling with my ex to avoid court, been there done that, a few years ago. I had the exact same opinion as you and I did not want to go to court. So I made a deal, even though knowing how she is, I was worried that she would come back for more in the future. And she did.
I am not too excited at the idea of paying more every three years just because she's asking for more in court with lies and false accusations. Sounds like extortion to me. To be honest, I am not thrilled about going to court, but I am not thrilled either about having the same dispute every 3 years. Once again nobody has a crystal ball, and perhaps in this case my rose-colored glasses turn into black-colored glasses, but I know how Bio Mom is and I was already proven correct once that she would ignore the deal and try to get more, so at this stage it will be more difficult to convince me that I won't be correct again about what would happen in 2021 if I settle financial issues now. Human beings tend to repeat their behaviors in the future. Not always, but more often than not, they do.
And regarding the children, Bio Mom has shown her true colors and now I see that without a court order she just takes advantage of the situation and does as she pleases, regardless of what the consequences are for children. That part of it, I did not expect her to do when I settled a few years ago.
By the way, my daughter told me last weekend that she had a fight with Bio Mom and ran away from the house a week ago (again) and that Bio Mom called police (again) to have her brought back home. And Bio Mom did not inform me of any of this. How is this going to be when she's a teenager? It's only going to get worse. And the worse the situation is at home, the stronger my resolve to ask for more access. If the situation was fine and dandy at home then I would not feel the need to disrupt the peace.