Child Support in North Carolina and Tx

My question involves child support in the State of: Tx and NC
I have a child support order but my childrens' father is in arreats for $156100. He recently obtained a work permit from immigration and his sister signed an affidavit of support (she owns numerous businesses in NC)....does that make her responsible for his child support as well? They live in NC, my husband, kids and I live in TX. Are grandparents in NC required to pay child support if he doesn't?

No, and no.

His sister will NEVER be responsible for his child support.

You can read this for further details. http://www.ncdhhs.gov/dss/cse/docs/csehandbook.pdf