I've represented a few Native children in child custody cases and they have to be enrolled in a tribe in order to be recognize mainstream court's child in need of assistance (CINA) cases.  There's time sensitive timelines that must be made in the first 24-48 hours of child removal from their homes under ICWA. It sounds like these children's mother made sure they were enrolled tribal members.  Therefore, the children's rights are protected under ICWA.  If the mainstream court in Texas and Alaska missed this requirement, then both court systems are in the wrong.  A good tribal lawyer can wrap this mess up and bring the children back to their tribe and family.