A couple uses a surrogate, with a clause that requires an abortion in certain circumstances. The surrogate was injected with fertilized eggs (e.g. only her uterus was used, none of her genetic material). The surrogate becomes pregnant with the couple's twins.
A medical issue is discovered. The couple requests an abortion, the surrogate refuses. The twins are born. The couple takes the twin with no medical issues, leaves the remaining twin with the surrogate.
Should the couple be responsible for child support for the child left with the surrogate?