Could I just go and pick up my children with a police escort or do I need an attorney?

I gave temporary guardianship to my children's father's (not legally married) twin brother due to a family emergency for 18 months. Ever since October of 2013, he and his wife have cut off all contact with the children becoming permanent since November of 2013.They promised me and their father that we would have contact with them and visitation, and totally went 180 since we made that agreement on paper. Then they took them and moved to another state before the agreement expired. Now it's expired, that family emergency has long been over and it's 2016. Approximately 3 years, our children have been away from us on August 3, 2016. Do I need to revoke the guardianship legally or get something in writing that would allow me to pick up my 6 children, and move on with our lives? They were and still are all minor children. Please help. I cannot afford an attorney right now even though I consulted with my aunt's and he did tell me that it looks like these people have stolen our children. Is there a reason I should get the authorities involved? I'd like a safe and peaceful return of our children.