How can we (non-custodial parents) protect the children before putting in a modication to a parenting plan?

My husband has a son from a previous marriage whom he is the non-custodial parent of in the parenting plan. However, over a year ago his ex-wife had a change in living situations and we gladly took my stepson and his brother (who is not my husband’s son) to live with us. They have now been living with us for over a year, but my husband is still paying monthly child support to his ex-wife even though she does not have the children or a place to live that she could support the child. We are afraid that if we push the matter she will take both boys out of our home and put them in dangerous situations since she had no home of her own, no job, and lives between two friends homes. Is there any legal action we can take on this matter?