Help me get my Kids from their evil dad

I lost my kids due to a default divorce. On purpose my now Exhusband sent the divorce papers to a wrong address. Now he is hiding in Kayenta on the Navajo Reservation. My kids are Lakota, he is a Caucasian and lives on the Navajo Nation which makes the whole case very complicated and that's why I need a lawyer. He says he takes care of my children, but in reality it is his sister and mother who do so - barely. He is out partying all the time especially on the weekends. My kids the are just beeing left behind or draged along with a bunch of drunks. I tried to have a civil arrangement with him, but since he is now smoking Potpurri, also known as Spice, K2 and synthetic marihuana, his attitude changes within seconds. I need to take my children out of this situation.