I think the child should be mortal.
I believe in the EPG it talks about how half-castes aer the result of the fetus being exposed to the essence, and their very being is changed.
If the child is a quarter-chaste it should be extremly weak.
Not quite...
The Sidereals chose their choice due to it being the easiest and safest path. So I think it would be more...
Natural course - 33.4% destruction of Creation
Bronze option (successful) - 25% Creation saved
Bronze option (unsuccessful) - 25% destruction of Creation
Gold...