Is killing one conjoined twin to save the other child murder?
Do they ever do that in the womb? It's my understanding that conjoined twins are usually separated after birth. Sometimes, long after birth.
Murder is an unlawful killing so it depends on the state of the law where the procedure occurs.
If you are asking whether it is wrong to purposely kill one to save the other, then yes, it is wrong. I am not saying that I would not do it, it would be a very hard choice indeed, but I believe it would be wrong!
No.
But killing someone for convenience is. Which is the rule of abortion. The exception where the mother's life is supposedly in danger is drastically overblown.