Secondly, even if we credit what the woman's wishes may be, and we know the husband's wishes - do we know the wishes of the only living being who's life is being decided by all these other people? As was stated above, there's no guarantee this developing child is in any way damaged, and even if he/she is there is no way of knowing the extent of that damage - as "nota bene"s post notes, there have been cases where a child has survived and thrived in such a situation. Even if we credit your assumption that the child will be damaged, who's to say that damaged child won't have a fulfilling and enjoyable existence if given the chance? Clearly, in comparison to yours or mine, the child's life may be far more physically and/or mentally challenging, but I don't know of many people who have been born with afflictions and wished they'd never been born. That's usually left to those who acquire an affliction after several years of "normal" life.
As for knowing what your own daughters want, if it's not in writing, giving you specific instructions, then you really don't know what they would be thinking or want at that crucial moment in time.