....that does strike Carissa as a strong argument for destroying Cheliax before his children might be ensouled, if they determine that those children exist and aren't ready to go ahead with the ascension plan yet. It could perhaps be done without prompting the gods to reassess Keltham as a threat if, instead of Wish wordings they need for the main plan, they use some lesser power out of dath ilan, or get some other countries to invade.
If solutions in that genre are not available, the arks that are meant to survive the destruction of Golarion should be equipped with the resources to resurrect the children and provide them a good life on the ark, and the Church of Iomedae equipped to sweep in, conquer Cheliax, and make it nice if it continues existing.
But crucially, this is not a problem Pharasma is going to be able to solve.
Pharasma probably hates the baby situation; Carissa has been reading up intensely on Pharasma and now infers it to be an ongoing source of annoyance to Hher, because babies don't have enough traits to be sorted. If She had a way to fix the baby situation Sshe would have done it. Playing hardball with Hher about the babies won't achieve anything, because the babies are a problem Pharasma wants solved, and which will be solved if the universe goes on existing through contraception and so on.
They have to come up with a clever and sufficient plan for protecting all of Keltham's babies which does not involve Pharasma at all, that's all there is to it.