Who should have the right to choose? Biological parents or surrogate mother?

A married couple who were TTC found out they had infertility issues and would not be able to naturally have a baby. They then decided to go with a surrogate to carry and birth the child for them. They found a surrogate and hired her, they then had their embryos placed in the surrogate mother. At some point through the pregnancy they found out that the baby will have major medical issues, complex heart conditions, a cyst in the brain, and a cleft palate and they couldn’t find a stomach or a spleen. After birth the baby would need several surgeries and was given a 25% chance of ever having a normal life. The doctor did give them the option to terminate the pregnancy.

The biological parents decided they wanted to terminate the pregnancy to save this baby from all the pain and suffering. They told their surrogate and she refused to do so, saying she is against abortion. They offered her $10,000 to do the abortion and she said she will only do it if they give her $15,000. The biological parents refused to pay her more.

The surrogate did sign a contract agreeing to abort if there were severe fetal abnormalities. The contract did not specify what is considered a severe fetal abnormalities so it can be argued that it’s not severe enough.

In a situation like this who should have the right to choose to terminate a pregnancy, the biological parents or the surrogate carrying the baby?

Edit- also the surrogate does not want to keep and raise the baby herself.