Will i get whatever is remaining from his backpay toward his 20,000 in arrear? Will i get a lump sum or installments. And will my daughter be eligibl

My daughters r 10 & 12. Their father is noncustodial parent n is 38. He's $20,000 in arrears. His last payent of child support was 01/2018. He got approved for disability n received first payment march 3. His monthly SSDI is $815.00. He told me all his back pay was garnished and got around 500.00 for his 1st payment. He was on cash assistance ovwr the past year or so but not sure exactly how long. I know welfare will get what he owes them first. Will i get whatever is remaining towards what he owes in arrears? And is is a lump sum or installments. And will my daughters be eligible for disability benefits as well? Noncustodial parent worked off and on since he was 15 yrs old. I have had primary full custody since 2011