Help my children get the last name they deserve

As most of you know I am a single mom raising 3 children on my own. I work two jobs to ensure my kids are taken care of. Birdie, Charlie and Goldie have recently showed interest in sharing my last name. They were born Greving’s. However they have nothing to do with that side of the family and their biological father has abandoned them. My family has filled in where needed and stepped up. My children should carry the last name of Kloss like me. Unfortunately to change their name comes at a cost. A cost I would go to the ends of the Earth to achieve, but I am only one person. I am 100% supporting my babies on my own. There is a court order for child support, but my ex falls short every month. He is currently $16K and counting behind and two years of no contact. My children deserve the last name Kloss and they want to have the same name as their mom. Please help me fund the process to make it happen. My children are Kloss’s. Help me legally make it happen.