What are the consequences If a individual refuses to respnd to a subpoena in a child support case?

I have two witnesses that will be subpoena in a child support case. Both can help my case; however, both are affraid to come to court. They say they will appear in court , but they haven't been arriving to court for the past couple of months for the court hearings. And now are not picking up my phone calls. One is my daughter and the other witness is the mother of the plantiff.

My daughter has never lived with her biological mother, she has been raised by her grandmother. And I have been ordered to pay child support to the mother of the child which I have been paying. But I do not want her to get my money. In matter in fact she lost custoidy to her other children. And the biological father of those kids has custody of them and she is paying child support for them.
My daughter is 19yr