If life begins at conception, what about parasitic twins?

it's two lives. And neither should be killed. What about babies born with no arms or with extra legs? They live fine. what about the Siamese twins? They are productive in society. If one is removed in order to make the other live, it's okay. But to abort them both so the parents don't have to deal with it, is wrong. every life has the right to live. No matter if it's for a minute or 100 yrs.