Why on earth would she pass of the child as her own child to family? Lies all over the place?
You could say "I do not agree with that. There will be no TTC unless we are all in accord. I am not bringing a child into this world in this manner."
Sounds like before TTC you all could talk about "being out" and what family support the new child and you each will have. And if you all choose to go forth WITHOUT family community support to bring a new child into being, you could go knowing exactly what you DO have resource wise and without hooha or surprises up ahead.
bring the kid into it. Not just what to call the parents, what to tell the extended relatives, or how to pay for prenatal and postnatal care, but how child custody would play out if this polyship folds later down the line. Already you think it isn't going to fly if there aren't changes.... so don't add another (baby) player to mix at this time til you talk all this stuff out.
Because IMO? I think it's poor family planning to raise a child in poor environmental health (physical environment and psychological environment) if you can prevent/improve upon it/sort it out beforehand. Dealing in children is time intenstive, and newborns with nursing moms -- that's super time intensive. Don't need drama on top.
Unwillingness to create a healthy space for a child to come into being and face problems... by telling new lies? That just smells of more problems down the road.
Big red flag. Tread with caution.
My 2 cents,