But think about how you would usually interact with a baby, dolly. You say the same sentence, but you change it, you make up little terms of endearment, you respond to what they are doing by saying something else.
-Come on then, poppet, up on the changing table This little piggy went to market, this little piggy stayed at home... let's see what's in the nappy after all, oh no it wasn't a poo, just a bit of wind, ooh that's a big burp, let's just clean you up a bit.....
And when you speak to a toddler, you are constantly shifting what you're saying:
-Look what's in there, look what's in the cage.
-Mousies.
-Yes, they're pretty mice, aren't they? What does the mouse say?
-MOOO.
-You silly moomoo, he doesn't, does he? The mouse says Squeak.
And so on ad infinitum. That is what normal mother-toddler interaction sounds like. But the OP specifically tells the mothers to stick to preset dialogues. (and I still don't get dialogues- surely that means two people speaking?)
Nothing wrong with teaching a child to read early. But wouldn't you be a bit about a programme designed to teach a baby to read early.
To my mind there are two ways with bilingualism:
You can interact with a baby but you can't formally teach them, in the sense that you teach a language to an adult. So it's interaction or nothing.
With an older child, you can either interact or teach (that is, explain things).
SO you can either start in babyhood and maybe modify your approach as the child grows, or if you insist on starting in babyhood, then you need to use age-appropriate measures.
To interact, you need far more knowledge of the language than you do to teach. I used to teach Spanish to adults and think I did a pretty good job of it, just explaining the principles. But I do not have enough Spanish to give it to a baby or toddler.
I think there is a risk of the OPs approach of stressing out the mums without actually achieving more than could have been achieved by waiting a few years and doing it in a different way.