Not the Dad, but paying child support

by JJ
(North Dakota)

My husband has 3 children from a previous marriage. The 2 oldest were born out of wedlock, and the youngest while him and his ex were married. They split up before the 2nd child was born and after a few months she told him she was pregnant and the 2nd child was his. He took her back and they got married a few months after he was born. While they were split up he did an at home paternity test and found out the oldest is his. During their divorce, while in a fight with him she told him that the 2 youngest children were not his. He signed all three birth certificates. He's paying child support on all three, but is a little behind. We live in North Dakota and wondering if we can have a court ordered paternity test done on the children, and if the test prove he's not the father will he still be held responsible for child support? Thank you for your help.